//After using session_destroy(), the session is destroyed behind the scenes. For some reason this doesn't affect the values in $_SESSION, which was already populated for this request, but it will be empty in future requests.

//You can manually clear $_SESSION if you so desire ($_SESSION = [];).
 <?php
 $_SESSION = [];
 session_unset();
 session_destroy();
?>

//make sure you don't forget to initialize session before destroying it
session_start() ;
session_destroy();
$_SESSION = [];//and clear it for this request