Personally, I use Araneae for all of my PHP programming (and Jscript, and HTML, and CSS.....I love this app!). It has a very clean interface, and contains plenty of features and options, without being bloated and overdone. There's nothing specific for PHP though.
However, if you're looking for a software package that is specifically for large PHP developments, Maguma Studio for PHP is one very cool PHP development environment. It can be integrated with a local PHP installation on your system (if you have one), and contains loads of PHP function libraries and code snippets. And as far as I know, it's FREE 😃