<?php
$number =  '8 (911) - 123 - 45 - 67';
$regExp = '/^ ?(8|\\+ ?7)([ \\-()]*[0-9]){10}$/';
$regSpace = '/[ ()\-]/';
$regCode = '/\\+7/';
if (preg_match($regExp, $number)) {
	$symbols = preg_replace($regSpace, '',$number);
	$code = preg_replace($regCode, '8', $symbols);
	echo $code;
} else {
	echo "Wrong number";
}