Currently RethinkDB has official drivers for three languages, Python, JavaScript, and Ruby. I hope you understand why it would be difficult for us to support many more than this. Eventually we're counting on support for 3rd party drivers from the community. In fact, there are already a few early community drivers from some intrepid contributors including for Haskell and Go.

We've had lots of requests for more drivers and lots of offers to build them, but we've asked our volunteers to hold off while we revamp the driver interface to make it significantly easier to build drivers for RethinkDB. Having written the first JS driver myself and the new version I can attest to the much greater ease of doing so with the new API.

The next release (1.4) due very soon will include these changes and a driver development kit to support 3rd party efforts. After that I'm sure you'll see a PHP driver emerge very quickly.