Phone Cases are not shown at FAA because it's a Pixels.com thing.
Everything you publish here is automatically listed also at Pixels.com. As long as you price it, phones cases will be listed, hopefully found by clients, and then finally sold via Pixels.com.
You find this info under Behind The Scenes --> Default Settings
Default Phone Cases Prices (for sale on Pixels.com)
When you upload a new image to Fine Art America, you can specify a default price for iPhone cases. If you use the same prices for all of your iPhone cases, this will save you a lot of typing and time after each upload...
However, you'll find everything on your artist's website.