In this recent post to PHPBuilder.com they spotlight a web-based tool you can use to write PHP code no matter where in the world you are - PHPanywhere.

PHP developers, just like most IT professionals, are often on the go, working from various locations. You could be working in your office one day, at a conference in a remote location the next day, and from a client's business office the next. [...] PHPanywhere is not just a stand-alone IDE, it's designed with project collaboration in mind. With a built-in FTP client and syntax editor built right in, it makes this tool uniquely appropriate for developer teams as well as individual programmers.

They look at how to get started with the tool and include a few screenshots to give you a preview of how the tool looks and feels. A short feature list is also included.