<?php

$url = "https:\/\/cdn1.vox-cdn.com\/thumbor\/zN9XawbQJgFPkuAcA2JEGgqApm8=\/cdn0.vox-cdn.com\/uploads\/chorus_asset\/file\/3700712\/tomorrowland54fdf04f23efb_2040.0.jpg" ;

echo str_replace("\\/", "/", $url);