If i remember right there was a button under Logs and Reports to view a sites php.log. Can’t find it there anymore. Running 7.20.2 Pro of Virtualmin.
Virtualmin --> PHP Error Log
Webmin --> System --> System Logs
How PHP logs depends on your execution mode.
But, if you’re using the recommended PHP-FPM, you should still have a PHP Error Log menu item in Logs and Reports, by default.