Jamie asks on LinkedIn.
The short answer
The question is wrong.
The long answer
A true PHP developer is a programmer who knows PHP. A false PHP developer is someone who doesn't know PHP. That's the closest correct answer I can think of.
I think, Jamie wants to ask, "what's your definition of a good PHP developer?". There is no correct answer to the question. All, you can do is highlight some of the good things a PHP developer does.
Let's seize this opportunity to talk about the traits of a good PHP developer. Most of the things that apply for a discussion about good PHP programmer also applies to a good web developer and good programmer in general.