If you run the server that came with Mamp, you should have a simple gui to enable and disable PHP. Of course you could do the same thing using the Apache that ships with OSX but you'd spend some time editing config files in terminal.
I would focus on running the free version of mamp. I know from experience it is easy to get apache up and running with full php support in under 10 minutes using mamp. Bear in mind, the apache server running in mamp runs on a different port than the default port 80 so if you're making changes to your mamp configuration and not seeing a change, make sure you are looking at the apache server that's running inside mamp and not the default apache server that came with OSX. That's one of the biggest time wasters in web development: Making changes on one server and refreshing a page coming from an entirely different server expecting to see a change.