We want to validate the Shopify checkout phone number field. Since we are using Pabbly to move customer data to our CRM, the country code needs to be included. To solve this, customers must enter their phone number with the country code in order to complete the order. If they skip the country code, they should be notified to add it before proceeding.
You can try our app Smart Checkout Plus.
It allows you to validate the checkout phone number field so that customers must enter their number with the country code before completing the order. If they skip the country code, they’ll get a prompt to add it and can only proceed once it’s correct.
Since you’re using Pabbly to sync customer data with your CRM, this will ensure all phone numbers are stored with the country code for smooth integration.
Hope this helps! 
You could try Ultimate Checkout Rules. You can add phone number validation and other checkout rules for your checkout using the AI assistant.