I know it's rhetorical but just to answer. No, in general phones increase bullying. Before phone and social media, bullied children would finish the school day and leave the bullying behind them. Now, it follows them on their phones with countless mocking messages... Messages like "X should kill himself for being so ...." and so on.
It makes the psychological part of any bullying that much more relentless.
In any case, the bully and the bullied will likely be separated for the rest of the day once the teacher is involved so the phone never needs to come into play.
What about if the kid's being bullied? Half the time the teacher will side with the bully, especially if the bully's a more popular kid.