How to Format Phone Numbers in Google Tag Manager (Web & Server) Using the Phone Number Formatter Variable

March 3, 2026

If you collect phone numbers through forms, checkouts, CRMs, or webhooks, you’ve likely noticed one issue:

Phone numbers are rarely stored in a consistent format.

Examples:

  • 07700 900123
  • +44 7700 900123
  • 0044 7700900123
  • (07700) 900123

When sending this data to CRMs, advertising platforms, or analytics tools like Google Analytics 4, inconsistent formatting can cause:

  • Failed user matching
  • CRM duplicates
  • Broken enhanced conversions
  • Hash mismatches

In this guide, you’ll learn how to standardize phone numbers in both web and server Google Tag Manager using the Phone Number Formatter variable, maintained by Stape.

Step 1: Understand What the Phone Number Formatter Does

The Phone Number Formatter variable:

  • Takes a raw phone number
  • Uses a country code (ISO 3166 format, e.g., GB, DK)
  • Converts it into E.164 format (international standard)

It uses Google’s phone number library to correctly interpret the number based on country rules.

⚠ Note: Currently supports European countries.

Step 2: Add the Correct Template from GTM Template Gallery

You need to download the appropriate version of the variable:

  • Web container version (for client-side GTM)
  • Server container version (for sGTM)

Step 3: Add the Template into Google Tag Manager

Inside your GTM container:

  1. Go to  variable Templates
  2. Go to template gallery and add it to workspace 

Step 4: Create the Phone Number Formatter Variable

Now create the actual variable:

  1. Go to Variables
  2. Click New
  3. Select Phone Number Formatter
  4. Configure the inputs:
    • Phone Number → Your raw phone number variable
      (Example: {{Form Phone}} or {{Event Data Phone}})
    • Country Code (ISO 3166) → Example: GB
  5. Click Save

Your formatter variable is now ready.

Step 5: Test the Output

Let’s say the input is:

Phone Number:

347660905435

Country Code:

GB

The output will be:

+44347660905435

That’s the standardized E.164 format.

Step 6: Use It in Your Tags

You can now use the formatted variable:

In Web GTM

  • Send it to enhanced conversions
  • Push it into the data layer
  • Use it in GA4 user properties

In Server GTM

  • Normalize phone numbers received via webhook
  • Format before hashing
  • Pass standardized numbers to APIs

Important: Format Before Hashing

If you plan to hash phone numbers (for example, SHA-256 for privacy compliance):

✔ Always format first
✔ Then hash

If you hash inconsistent formats, user matching will fail.

Correct sequence:

Raw Number → Format → Hash → Send to platform

When Should You Use Phone Number Formatter?

Use it when:

  • You collect phone numbers from multiple sources
  • You send phone numbers to ad platforms
  • You use enhanced conversions
  • You sync data with a CRM
  • You handle phone numbers in server-side tracking

It ensures consistency across your entire data pipeline.

Final Thoughts

Phone numbers may seem like a small detail — but inconsistent formatting can reduce match rates and break integrations.

By following these steps, you can:

  • Standardize phone numbers
  • Improve CRM accuracy
  • Increase advertising match rates
  • Keep your tracking clean and reliable

If you’re working with user identifiers inside Google Tag Manager, the Phone Number Formatter variable is a simple yet powerful addition to your setup.