I seriously doubt that there is a PHP release for the Palm OS. I don't think there will ever be one. There is limited disk space with the Palm, and the processing power isn't enough.
If you know how the palm works, you'll understand. If not, see below...
When you start your Palm, the OS "boots up" and you are brought to your home screen. Well, when you choose an application to run, it's already running, but brought to the focus of the palm. So your always running your apps, but not in focus. So the processor takes quite a load eventually.
PHP on a Palm would be useless from wha I can tell. And to store mySQL databases on a Palm OS aren't that good either, space issue. Unfortunately you'll have to use some work around like an excel sheet, or another database app.
~Brett