diff --git a/packages/features/ee/workflows/lib/reminders/templates/customTemplate.test.ts b/packages/features/ee/workflows/lib/reminders/templates/customTemplate.test.ts
new file mode 100644
index 0000000000..ceb0be21e0
--- /dev/null
+++ b/packages/features/ee/workflows/lib/reminders/templates/customTemplate.test.ts
@@ -0,0 +1,151 @@
+import { describe, expect, it } from "vitest";
+import customTemplate, {
+  formatIdentifierToVariable,
+  getVariableFormats,
+  transformBookingResponsesToVariableFormat,
+} from "./customTemplate";
+
+describe("formatIdentifierToVariable", () => {
+  it("should convert spaces to underscores and uppercase", () => {
+    expect(formatIdentifierToVariable("Company Name")).toBe("COMPANY_NAME");
+  });
+
+  it("should preserve existing underscores", () => {
+    expect(formatIdentifierToVariable("Company_Name")).toBe("COMPANY_NAME");
+  });
+
+  it("should handle multiple underscores", () => {
+    expect(formatIdentifierToVariable("Monthly_Infrastructure_Spend")).toBe("MONTHLY_INFRASTRUCTURE_SPEND");
+  });
+
+  it("should remove special characters except underscores", () => {
+    expect(formatIdentifierToVariable("Company-Name!")).toBe("COMPANYNAME");
+  });
+
+  it("should handle mixed spaces and underscores", () => {
+    expect(formatIdentifierToVariable("Company_Name Here")).toBe("COMPANY_NAME_HERE");
+  });
+
+  it("should trim whitespace", () => {
+    expect(formatIdentifierToVariable("  Company Name  ")).toBe("COMPANY_NAME");
+  });
+  it("should preserve numbers", () => {
+    expect(formatIdentifierToVariable("Company123_Name")).toBe("COMPANY123_NAME");
+  });
+});
+
+describe("getVariableFormats", () => {
+  it("should return both formats when identifier has underscores", () => {
+    const formats = getVariableFormats("Company_Name");
+    expect(formats).toContain("COMPANY_NAME");
+    expect(formats).toContain("COMPANYNAME");
+    expect(formats).toHaveLength(2);
+  });
+
+  it("should return single format when no underscores in identifier", () => {
+    const formats = getVariableFormats("Company Name");
+    expect(formats).toEqual(["COMPANY_NAME"]);
+  });
+
+  it("should return single format when identifier has no special chars", () => {
+    const formats = getVariableFormats("CompanyName");
+    expect(formats).toEqual(["COMPANYNAME"]);
+  });
+
+  it("should handle multiple underscores", () => {
+    const formats = getVariableFormats("Monthly_Infrastructure_Spend");
+    expect(formats).toContain("MONTHLY_INFRASTRUCTURE_SPEND");
+    expect(formats).toContain("MONTHLYINFRASTRUCTURESPEND");
+    expect(formats).toHaveLength(2);
+  });
+});
+
+describe("customTemplate - variable replacement", () => {
+  const baseVariables = {
+    eventName: "Test Event",
+    organizerName: "Test Organizer",
+    attendeeName: "Test Attendee",
+    timeZone: "UTC",
+  };
+
+  it("should replace variables with underscores in template", () => {
+    const responses = transformBookingResponsesToVariableFormat({
+      Company_Name: { value: "Acme Corp", label: "Company Name" },
+    });
+
+    const result = customTemplate(
+      "Company: {COMPANY_NAME}",
+      { ...baseVariables, responses },
+      "en",
+      undefined,
+      true
+    );
+
+    expect(result.text).toBe("Company: Acme Corp");
+  });
+
+  it("should replace legacy variables without underscores in template (backward compatibility)", () => {
+    const responses = transformBookingResponsesToVariableFormat({
+      Company_Name: { value: "Acme Corp", label: "Company Name" },
+    });
+
+    const result = customTemplate(
+      "Company: {COMPANYNAME}",
+      { ...baseVariables, responses },
+      "en",
+      undefined,
+      true
+    );
+
+    expect(result.text).toBe("Company: Acme Corp");
+  });
+
+  it("should handle both variable formats in the same template", () => {
+    const responses = transformBookingResponsesToVariableFormat({
+      Company_Name: { value: "Acme Corp", label: "Company Name" },
+      Monthly_Spend: { value: "$5000", label: "Monthly Spend" },
+    });
+
+    const result = customTemplate(
+      "Company: {COMPANY_NAME}, Spend: {MONTHLYSPEND}",
+      { ...baseVariables, responses },
+      "en",
+      undefined,
+      true
+    );
+
+    expect(result.text).toBe("Company: Acme Corp, Spend: $5000");
+  });
+
+  it("should handle identifiers with spaces (converted to underscores)", () => {
+    const responses = transformBookingResponsesToVariableFormat({
+      "Company Name": { value: "Acme Corp", label: "Company Name" },
+    });
+
+    const result = customTemplate(
+      "Company: {COMPANY_NAME}",
+      { ...baseVariables, responses },
+      "en",
+      undefined,
+      true
+    );
+
+    expect(result.text).toBe("Company: Acme Corp");
+  });
+
+  it("should handle array values", () => {
+    const responses = transformBookingResponsesToVariableFormat({
+      Selected_Options: { value: ["Option A", "Option B", "Option C"], label: "Selected Options" },
+    });
+
+    const result = customTemplate(
+      "Options: {SELECTED_OPTIONS}",
+      { ...baseVariables, responses },
+      "en",
+      undefined,
+      true
+    );
+
+    expect(result.text).toBe("Options: Option A, Option B, Option C");
+  });
+});
diff --git a/packages/features/ee/workflows/lib/reminders/templates/customTemplate.ts b/packages/features/ee/workflows/lib/reminders/templates/customTemplate.ts
index 0c5bf3768a..f02a5587d9 100644
--- a/packages/features/ee/workflows/lib/reminders/templates/customTemplate.ts
+++ b/packages/features/ee/workflows/lib/reminders/templates/customTemplate.ts
@@ -56,6 +56,19 @@ export function transformRoutingFormResponsesToVariableFormat(
 }
 
 export function formatIdentifierToVariable(key: string): string {
+  return key
+    .replace(/[^a-zA-Z0-9_ ]/g, "")
+    .trim()
+    .replaceAll(" ", "_")
+    .toUpperCase();
+}
+
+/**
+ * Legacy version of formatIdentifierToVariable that strips underscores.
+ * Used for backward compatibility with templates that were created when
+ * underscores were being stripped from identifiers.
+ */
+function formatIdentifierToVariableLegacy(key: string): string {
   return key
     .replace(/[^a-zA-Z0-9 ]/g, "")
     .trim()
@@ -63,6 +76,22 @@ export function formatIdentifierToVariable(key: string): string {
     .toUpperCase();
 }
 
+/**
+ * Returns all variable formats for a given key.
+ * Includes both the current format (with underscores preserved) and the legacy format
+ * (without underscores) for backward compatibility with existing templates.
+ * @returns Array of unique variable formats
+ */
+export function getVariableFormats(key: string): string[] {
+  const current = formatIdentifierToVariable(key);
+  const legacy = formatIdentifierToVariableLegacy(key);
+
+  if (current === legacy) {
+    return [current];
+  }
+  return [current, legacy];
+}
+
 export type VariablesType = {
   eventName?: string;
   organizerName?: string;
@@ -196,9 +225,13 @@ const customTemplate = (
     // handle custom variables from form/booking responses
     if (variables.responses) {
       Object.keys(variables.responses).forEach((customInput) => {
-        const formatedToVariable = formatIdentifierToVariable(customInput);
+        const foundVariableInTemplate = variable;
+        const availableVariable = formatIdentifierToVariable(customInput);
+        // Legacy format for backward compatibility with templates created before underscore support
+        const availableVariableLegacyFormat = formatIdentifierToVariableLegacy(customInput);
+        const isFoundTemplateVariableValid = foundVariableInTemplate === availableVariable || foundVariableInTemplate === availableVariableLegacyFormat;
 
-        if (variable === formatedToVariable && variables.responses) {
+        if (isFoundTemplateVariableValid && variables.responses) {
           const response = variables.responses[customInput];
           if (response?.value !== undefined) {
             const responseValue = response.value;
@@ -206,7 +239,7 @@ const customTemplate = (
               ? responseValue.join(", ")
               : String(responseValue);
 
-            dynamicText = dynamicText.replace(`{${variable}}`, valueString);
+            dynamicText = dynamicText.replace(`{${foundVariableInTemplate}}`, valueString);
           }
         }
       });
diff --git a/packages/features/tasker/tasks/executeAIPhoneCall.test.ts b/packages/features/tasker/tasks/executeAIPhoneCall.test.ts
new file mode 100644
index 0000000000..df1f8a1370
--- /dev/null
+++ b/packages/features/tasker/tasks/executeAIPhoneCall.test.ts
@@ -0,0 +1,85 @@
+import { convertResponsesToVariableFormats } from "@calcom/features/tasker/tasks/executeAIPhoneCall";
+import { describe, expect, it } from "vitest";
+
+describe("executeAIPhoneCall - convertResponsesToVariableFormats", () => {
+  it("should generate both variable formats for identifiers with underscores", () => {
+    const responses = {
+      Company_Name: { value: "Acme Corp" },
+      Monthly_Infrastructure_Spend: { value: "$5000" },
+    };
+
+    const variables = convertResponsesToVariableFormats(responses);
+
+    // Should have both underscore and non-underscore versions
+    expect(variables.COMPANY_NAME).toBe("Acme Corp");
+    expect(variables.COMPANYNAME).toBe("Acme Corp");
+    expect(variables.MONTHLY_INFRASTRUCTURE_SPEND).toBe("$5000");
+    expect(variables.MONTHLYINFRASTRUCTURESPEND).toBe("$5000");
+  });
+
+  it("should generate single format for identifiers without underscores", () => {
+    const responses = {
+      "Company Name": { value: "Acme Corp" },
+      Email: { value: "test@example.com" },
+    };
+
+    const variables = convertResponsesToVariableFormats(responses);
+
+    // Space-separated identifiers convert to underscore format
+    expect(variables.COMPANY_NAME).toBe("Acme Corp");
+    // Simple identifiers stay as-is
+    expect(variables.EMAIL).toBe("test@example.com");
+  });
+
+  it("should handle mixed identifiers correctly", () => {
+    const responses = {
+      Company_Name: { value: "Acme Corp" },
+      "Contact Email": { value: "contact@acme.com" },
+      Notes: { value: "Some notes" },
+    };
+
+    const variables = convertResponsesToVariableFormats(responses);
+
+    // Underscore identifier: both formats
+    expect(variables.COMPANY_NAME).toBe("Acme Corp");
+    expect(variables.COMPANYNAME).toBe("Acme Corp");
+
+    // Space identifier: single format (space becomes underscore)
+    expect(variables.CONTACT_EMAIL).toBe("contact@acme.com");
+
+    // Simple identifier: single format
+    expect(variables.NOTES).toBe("Some notes");
+  });
+
+  it("should preserve the same value for both variable formats", () => {
+    const testValue = "Test Value 123";
+    const responses = {
+      Test_Field: { value: testValue },
+    };
+
+    const variables = convertResponsesToVariableFormats(responses);
+
+    expect(variables.TEST_FIELD).toBe(testValue);
+    expect(variables.TESTFIELD).toBe(testValue);
+    expect(variables.TEST_FIELD).toBe(variables.TESTFIELD);
+  });
+
+  it("should handle empty responses", () => {
+    const responses = {};
+
+    const variables = convertResponsesToVariableFormats(responses);
+
+    expect(Object.keys(variables)).toHaveLength(0);
+  });
+
+  it("should handle undefined values", () => {
+    const responses = {
+      Field_Name: { value: undefined },
+    };
+
+    const variables = convertResponsesToVariableFormats(responses);
+
+    expect(variables.FIELD_NAME).toBe("");
+    expect(variables.FIELDNAME).toBe("");
+  });
+});
diff --git a/packages/features/tasker/tasks/executeAIPhoneCall.ts b/packages/features/tasker/tasks/executeAIPhoneCall.ts
index 21cfbbb7cd..7c924dd5c6 100644
--- a/packages/features/tasker/tasks/executeAIPhoneCall.ts
+++ b/packages/features/tasker/tasks/executeAIPhoneCall.ts
@@ -3,7 +3,7 @@ import dayjs from "@calcom/dayjs";
 import { getCalEventResponses } from "@calcom/features/bookings/lib/getCalEventResponses";
 import { createDefaultAIPhoneServiceProvider } from "@calcom/features/calAIPhone";
 import { handleInsufficientCredits } from "@calcom/features/ee/billing/helpers/handleInsufficientCredits";
-import { formatIdentifierToVariable } from "@calcom/features/ee/workflows/lib/reminders/templates/customTemplate";
+import { getVariableFormats } from "@calcom/features/ee/workflows/lib/reminders/templates/customTemplate";
 import { WorkflowReminderRepository } from "@calcom/features/ee/workflows/lib/repository/workflowReminder";
 import { FeaturesRepository } from "@calcom/features/flags/features.repository";
 import {
@@ -14,7 +14,6 @@ import { checkRateLimitAndThrowError } from "@calcom/lib/checkRateLimitAndThrowE
 import logger from "@calcom/lib/logger";
 import prisma from "@calcom/prisma";
 import { CreditUsageType } from "@calcom/prisma/enums";
-
 interface ExecuteAIPhoneCallPayload {
   workflowReminderId: number;
   agentId: string;
@@ -35,6 +34,23 @@ type BookingWithRelations = NonNullable<
   >["booking"]
 >;
 
+/**
+ * Converts responses to variable format entries with both current and legacy formats
+ * for backward compatibility.
+ * Accepts both FORM_SUBMITTED_WEBHOOK_RESPONSES and CalEventResponses types.
+ */
+export function convertResponsesToVariableFormats(
+  responses: Record<string, { value?: unknown }>
+) {
+  return Object.fromEntries(
+    Object.entries(responses).flatMap(([key, value]) => {
+      const formats = getVariableFormats(key);
+      const valueStr = value.value?.toString() || "";
+      return formats.map((format) => [format, valueStr]);
+    })
+  );
+}
+
 function getVariablesFromFormResponse({
   responses,
   eventTypeId,
@@ -52,13 +68,8 @@ function getVariablesFromFormResponse({
     ATTENDEE_EMAIL: submittedEmail || "",
     NUMBER_TO_CALL: numberToCall,
     eventTypeId: eventTypeId?.toString() || "",
-    // Include any custom form responses
-    ...Object.fromEntries(
-      Object.entries(responses || {}).map(([key, value]) => [
-        formatIdentifierToVariable(key),
-        value.value?.toString() || "",
-      ])
-    ),
+    // Include custom form responses with both current and legacy variable formats for backward compatibility
+    ...convertResponsesToVariableFormats(responses || {}),
   };
 }
 
@@ -102,13 +113,8 @@ function getVariablesFromBooking(booking: BookingWithRelations, numberToCall: st
       .format("h:mm A"),
     // DO NOT REMOVE THIS FIELD. It is used for conditional tool routing in prompts
     eventTypeId: booking.eventTypeId?.toString() || "",
-    // Include any custom form responses
-    ...Object.fromEntries(
-      Object.entries(responses || {}).map(([key, value]) => [
-        formatIdentifierToVariable(key),
-        value.value?.toString() || "",
-      ])
-    ),
+    // Include custom form responses with both current and legacy variable formats for backward compatibility
+    ...convertResponsesToVariableFormats(responses || {}),
   };
 }