What sorts of questions do I need to ask a PHP programmer I want to hire to know if he/she is good?

I can help you out with this!

Ask for industry certifications. The 2 industry certifications for PHP are the Zend Certified Engineer in PHP5 certification and also the Zend Certified Engineer w/ Zend Framework. The ladder of the 2 is more of a supplemental certification.

Also ask if they utilize any "frameworks" to write their applications with. You want the answer to be yes. Frameworks for rich web applications force web projects into a strict structure which makes them more robust and less prone to error.

You will want to make sure they use the software architecture called "Object-Oriented Programming (OOP)". Good software architects will tell you there is no better method to use. People who do not use OOP structures end up with, what we call in the business, spaghetti code. Spaghetti code essentially is one long page with 4000+ lines of code which is a maintenance nightmare.

You will want to ask what version of PHP they are using. To keep with the times, PHP 5.2 or newer is the only acceptable version. If they are programming in PHP4, they are way behind the times because PHP4 is practically archaic now-a-days.

Ask how familiar they are with proper PHP secure programming. If they mention some of the following, they are squared away: Validation, Filtering, Cross-site scripting attacks, SQL Injection, Remote Code Injection, Request Forgeries, or Session Hi-jacking.

If you choose, you will want to ask for previous work history. Make sure this is not their first project(unless you are getting a good deal, it may be worth it then).

Finally, make sure they speak english and have a cell phone. I know this may seem strange but, it's important.

Anyways, Good luck in your search. Perhaps if all else fails, you can just hire me =D.

Take care!
Brian