I would consider myself to be at an intermediate level of php coding, I can do all the basic stuff in php, connecting to database, includes, functions, arrays, etc. However I would really like to elevate my knowledge of the language to a more advanced level.
Does anyone have any suggestions for books or classes online I could take a look at? Or should I just focus on perfecting the skills I already have?
I have been looking at some of the books on amazon but they seem to just cover stuff I already know.
If you're at such a high level of coding, do some freelancing stuff, advertise yourself on php freelance websites & hone your skills to a more conversant level.
From the stuff you mentioned, this all is as you say "basic stuff..", if you want elevation in your coding/programming practices/standards, investigate more into OOP as this is what industry looks for. Procedural is fine; but companies are looking for people who can work on OOP projects, this just makes things run so much better.
Other than that, get some books from 'tinternet and find yourself a project that you can really get your teeth into.
An honestly, Zend offer good things too.
And above all there is always something else to learn - after all you never stop.