<?php

$rawPhone = "+7(123 123-45 67";

$regExpProper = '/(?:8|\\+7)((?:[\\s\\(\\)\\-]*[0-9]){10})/';
preg_match_all($regExpProper, $rawPhone, $matches);

$regExpClean = '/[^0-9\\+]/';
$cleanPhone = preg_replace($regExpClean, "", $matches[1][0]);

$properPhone = "8{$cleanPhone}";

echo $properPhone;