How to write regular expression for following conditions:
So for I can do only for first two conditions. I am not sure how to do the third conditions My code is
if (!preg_match('/^[0-9]{8}$/', $number))
You're almost there. Simply remove the first number from the character class and validate it at the start of your pattern...
/^(8|9|6)\d{7}$/
FYI - \d is the escape sequence for digits. I suppose you could also use this
/^[896]\d{7}$/
as it means about the same thing when you're only watching for a single character at the start.