Danielle,
Its not a trifling move. Its one of those things where if you have to ask, you probably can't do it.
Most users of a phone would be annoyed by having to scroll down past the menu on every page in order to see content.
Imagine I click on the RC cars category. At the top of the page on a mobile device, I had better see an RC car, or some textual information related to the subject. The last thing I want to see is the same category menu I just clicked, and have to scroll the screen in order to see it.
The way this is handled better, is to display the categories in a touch menu with 3 bars across, and sticky that to the top of the page. Like this:
http://xcartnext.com/