Okay, I've created a brief introduction to Phex filter rules, and how to use them:

http://www.phex.org/wiki/index.php/Filter_System

I included plenty (!!) of screen captures, and started out by using an example of wanting to search for music video files over a certain size, followed by showing how to further limit results to just videos. Also included brief example of filtering by words in the 'file' column.

If something isn't clear, or I managed to confuse the heck out of folks, let me know and I'll be glad to tune things some more.