On Developer.com there's a recent tutorial looking at developing your first Andriod application in PHP (running in a PHP interpreter on your device).

Google's open source Android mobile operating system is taking the smartphone market by storm. Unlike Apple, which has stringent guidelines and requirements for developers who want to offer their applications on the iPhone App Store, Google has left the Android platform wide open. You can even write Android applications in PHP now. The folks at Irontech have created a PHP port to run on Android, and with the Scripting Layer for Android (SL4A), you can build PHP Android applications.

He shows you how to install the tool on your emulator (it doesn't have to be on a device) and how to set up the PHP environment to work with the SDK. He also includes some sample code to help you get started - an interface to the take88.com. There's also instructions on how to get the mini-application working on your phone.