When I boot up my computer and my phone is charging or something via usb, a message comes up that forces me to press f1 to continue, due to the boot priority changing. I'm on a nforce 750i motherboard from evga and can't find a way to turn it off in the bios.
Unfortunately, you can't do this. I have the same motherboard. The reason it pops up is that a new mass-storage device has been detected - similar to if you changed the hard drives or added a new one.
What phone is it? Try connecting the phone NOT in "mass-storage" mode, and see what happens.
Another possibility is to disable the "Keyboard wait on error" setting in the BIOS...