I own an original NES, a copy of Tetris, Dr. Mario, and SMB1. If I'm ever using my NES, I usually spend my time playing Tetris so to get my fix of Dr. Mario, I play on my phone when I have downtime (on the bus, between classes, during less important lectures, etc.). Usually I play level 14 to practice for the DM Championships or try to reach level 24 and loop it a few times. More recently, however, I wanted to give 0-10 speedruns a try. My first submission was rejected on account of "phone emulators is not allowed." Why is this? PC emulation is allowed and I'm using a legal copy of the ROM.

I'm not sure, but I've heard that phone emulators are not accurate.

Phone emulation is not allowed for emulation because they are notoriously inaccurate. That's pretty much all there is to it.