There are many ways to add a cron job that calls a php script - and it really depends on how your server is setup.

Here’s some example setups:

/usr/local/bin/php /home/user/public_html/script.php

lynx -dump http://www.example.com/script.php

/usr/bin/curl http://www.example.com/script.php

I found out about the last way of loading a cron with a php script because the lynx version was giving me permission errors and the /usr/local/bin/php method just wouldn’t work.