Depends what the situation is.

I have the CS3 professional pack, so I'll use dreamweaver on a lazy day, or if the php is apart of what I'm making.
If the php is just a small text file (say for integration with something), I'll just use notepad.

If I am editing a file on my server, I load up File Manager v3, and use its text editor, but if theres a syntax error I'll use the code editor.

As my teacher always says, 'the best piece of software is the one that works for you'.