You could use /scripts/easyapache - which is the easiest way to go. Otherwise you would need to download the source for all modules and compile them manually. No matter which of the two you choose, if you've never done it before (and have never manually compiled something from source) it may be better to pay an admin and ask them to walk you through it first time. It can get hairy if you have lots of people relying on the box... GL!
As webtiva mentioned, you'll want to run /scripts/easyapache, then select the Advanced option (#6), go down and enter the PHP module sub-menu, and select themodules you would like compiled into PHP. Exit from both submenus, save the changes, and then watch it blast away.