On SoftDevTube.com they've posted a new tutorial screencast talking about how you can write Flex and PHP inside Flash Builder and Zend Studio.
This video explains how to write Flex and PHP code using Flash Builder 4 and Zend Studio 7.1. It also illustrates how remoting enables your application to consume PHP services.
The video's about ten minutes long and comes from Adobe TV. There's no way to download the sample application they create, but they walk you through all of the steps you'll need, right down to getting PHP integrated into Flash Builder.