Only php IDE. Code highlighting isn't enough. And how about outocomplete, navigation through the project?
And the most helpful - Debugger?! I can't imagine editor with these features.
That's why I prefer such php EDIs as Codelobster php Edition and Zend.
I suggest to try them:
Codelobster php Edition -
www.codelobster.com
Zend -
www.zend.com