You can create a phpinfo.php file on your domain’s htdocs folder with this content:
<?=phpinfo()?>
and when you visit it through your browser it should show the PHP version and all the extensions enabled on that PHP version and the technical info as well.
Visit your control panel (CPanel) and click Account Settings on the top, then scroll down to PHP Settings at the bottom of the page, it’ll tell you the PHP Version.
But that info is hardcoded and always says 7.4.8; when you create a file with that content instead you should see the actual PHP version the server that hosts your website has. Anyway, now that the IP addresses of the nameservers are down, I also doubt he can access it afterwards for now, so he also needs to wait until the DNS problem gets fixed.
EDIT: Now the nameservers are back up (at least for now).