Is your php code returning 500 Internal Server Error instead of PHP erros page?

Lets try this header in the first lines of your .php page:

<?php

error_reporting(E_ALL);
ini_set('error_reporting', E_ALL);
ini_set('display_errors', 1); 
ini_set('display_startup_errors', 1);

?>

You can also edit your

/etc/php.ini

with this parameters to make this settings permanent.