Validation for a 10 digit phone number

/[2-9]{2}\d{8}/

^[2-9]{2}[0-9]{8}$

I consider [0-9] to be better to read than \d, especially considering the preceding [2-9]

The ^ and $ ensure that the input string consists ONLY of those 8 characters - otherwise it is not guaranteed that the input string is not larger - i.e. "12345678901" would match the regex w/o those two characters - although it is 11 chars and starts with a 1!