<?php
$test = ['07511 111111', '+447511 111111', '+44 (0) 7511 111111', '07211 111111', '3749853857', '0712121211233'];
foreach ($test as $input) {
//step 1 - reduce it to digits:
preg_match_all('([\+]{0,1}[^\(\) ][0-9]+)', $input, $digits);
$digits = implode($digits[0]);
//now for step 2.. start by removing +44 and replacing it with 0
if (substr($digits, 0, 3) == '+44')
{
$digits = str_replace('+44', '0', $digits);
}
//by this point we should have just a UK-style number, but we must validate it:
if ((substr($digits, 2, 1) > 3) && strlen($digits) == 11)
{
//valid UK mobile number!
echo "\nValid UK mobile number $digits";
}
}