Sunucunuzda fopen açıksa şöyle:
<?php echo file_get_contents('https://xxx.com/url.php'); ?>
Curl açıksa şöyle:
<?php
$ch = curl_init('https://xxx.com/url.php');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
echo curl_exec($ch);
?>