Vinu Thomas talks about a platform on his blog today that can be used to create PHP applications to live on a S60 phone.
If you'd like to work on your favorite PHP apps on your S60 phones, here's PAMP - Personal Apache, MySQL and PHP. This is implemented on the Symbian OS using Open C, which is a set of industry-standard POSIX and middleware C libraries for S60.
The PAMP system is pretty easy to install and guides can be found over on the dev.mobi website to help get you started. You can download the latest version of the project from its SourceForge website.