In order for PHP to be most useful, it should have as many of the modules installed as will be used. I recommend installing it using the FPM sapi, which manages php session spawning.
The `PHP_TARGETS` setting in `/etc/make.conf` lets you select which versions of PHP to compile. If possible, I recommend always using the latest stable version.
As of the time this is written, php 5.3 is the latest version, so I would add this line to `/etc/make.conf`
`PHP_TARGETS="php5-3"`
As of this writing, PHP compiles with clang reliably.