What kind of PHP specializations are there?
You mean like frameworks... or what?
As a job. I can only think of a few; online commerce systems, regular backend website development, database management.
I'd like to work as a PHP programmer and wondered what areas I could go into.
Really you don't decide what you do, it's the company needs that decide. So you have to see if there's a lot of php need in your area.
I love programming php but my expertise is dot net because most business uses dot net. So sadly it's not what you like but what it's needed. I still do php at home though
I believe PHP specialization is in web. If you want more diversity than Java/.NET is a good choice.