can't find PHP source folder



I want to install MagickWand on my system. Therefore I need to place some files in the PHP source folder. But the problem is that i can't find that folder.
PHP is working as it should.

I don't have usr/local/php4, nor such a folder in etc/.

PHP module is in libexec/httpd/

I have a php.ini.default in etc/

I don't remember how I activated/installed PHP, so I don't know where everything is gone.

Anyone some suggestions where to look?
Otherwise how to disable/ uninstall PHP so that I can configure everything from the beginning?