If no "php bindings" exist, it looks like you'll have to develop them ;-)
This is done via a PHP extension -- such as, for example :
- the
mysql
extension, that's used to communicate with MySQL, binding the libmysql library (with PHP <= 5.2)
- The
curl
extension, that's a wrapper arround the curl library
- and so many others...
If you want to learn more about writing PHP extensions, those links will probably interest you :
(Note that it's not quite an easy task -- but if you are required to... well ^^ ; and some would say it's not that hard )
And, if you are really interested by the subject, and ready to spend some money on it, you could buy the book Extending and Embedding PHP (some pages are available as preview on Google Books too) ; It's considered as the book to read when interested on this subject (In fact, I've bought it some time ago, and, in my opinion, it is indeed an interesting read)
BTW, the author of that book is also the author of the first four articles I linked to ;-)