Use the prop removal tool that came with your phantom. If that doesnt work, dont use a pliers because it will crush your motor. Make sure you are taking it off in the correct direction.
If you still cant get it off, try wrapping the motor with duct tape, and try it again.
After you get the prop off, try spinning on a new one. If it doesnt spin almost all the way on, you might have a bent motor shaft.