<?php
    $num = '+ 79--35(- 358741()3';
    $numClean = preg_replace ('/[)(\s+-]*/',"",$num);
    if (mb_strlen($numClean)>11){ 
    	exit ("THIS IS A MISTAAAKE");
    }
     $finishedNum = preg_replace ('/^[7]/',8,$numClean);
    echo "$finishedNum";