Sounds to me like PHP is not running on your system, or (perhaps) an older version of PHP.
But you can check PHP status by creating a simple PHP file with the command
phpinfo();
in it and loading that page in your browser. That should show you the current settings of PHP, if it is running. And perhaps check with your hosting support to see what they say.
There are many googles/bings/ducks about how to ensure PHP is running on your server. I’d start there.