how to validate first three digits of phone number

Question

I have a TextFormField for a phone number and I want to validate the input to match my RegEx to phone number value

the valid inputs are

075xxxxxxxx
077xxxxxxxx
078xxxxxxxx
079xxxxxxxx

I tried this r"^ (?:[0]7)?[0-9]{11}$" but its not working

any way to do it right?

Answer 1

Match a zero, then a 7, then any of [5,7,8,9] then any 8 digits:

07[5789]\d{8}