Sorry for the really late reply. I also didn't know why they were banned, so I looked it up and here is the reasoning from a GDQ organizer:
"Phone emulators use various speed hacks, frame skipping, etc. PC emulators don't really do that anymore, it's not needed. But when your inaccurate smartphone emulator doesn't have any in-game lag due to all the (sometimes intentional) inaccuracies, it gives them a big benefit.
Star Fox is a great example. An accurate emulator will keep the slow, laggy frame rate of the original console. An inaccurate one will play much faster."
Basically, smartphone emulators are less accurate and use various hacks, both of which would give an advantage to players on these devices.
So if someone were to make a run category for Star Fox only on these inaccurate mobile emulators, it would be faster than a normal any%?