On the Adobe Developer Connection there's a recent tutorial posted looking at combining PHP and Flex to make a simple charting application.

One area in which Flex and PHP go really well together is in creating data visualizations. PHP makes it incredibly easy to retrieve information from a database and manipulate it. For its part, Flex provides a user interface layer that is interactive and capable of quickly calculating shapes, which is perfect for charting.

The article focuses on the structure of the data between the PHP application and the Flex frontend (since it needs a bit more definition than some of the usual PHP methods for plotting charts). The files needed to follow along with the tutorial are available for download as well as links to try or buy Flash Builder. In the end, you'll have a chart like this for your efforts.