I would recommend just following our Caddy install docs:
and then follow your favorite PHP install tutorial. Telling Caddy to forward to your PHP app is one line:
php_fastcgi localhost:7000
(where :7000 is your php-fpm listener)
Although, I’m rather a big fan of FrankenPHP:
FrankenPHP does not require php-fpm as it’s all built-in to Caddy directly.