How it would be disappointed if you received an order but cannot contact the customer with the phone number? How to avoid customers entering wrong phone number? With the following steps you may do phone number validation in gravity forms now.
With our plugin Gravity Forms Blacklist and Custom Validation you may create a custom validation list with the following rules.
1. Limit customers can only enter number for phone number.
2. Phone number has a fixed length and you may require the phone number length must exactly same as you want.
3. Phone number has a fixed start for special area and you may set it start with "1" or others.
And then apply the custom validation to the phone number field in gravity forms editing screen.