I find having ridden up to the drivers door without them noticing and then banging hard on the drivers window and tell them repeatedly to put their phone down has quite an effect, and hopefully makes them more wary of using them in future (I am an optimist!).
It certainly worked last saturday, as she had no idea that she was a) drifting into the middle of the road and b) had been caught up
Of course in reality its likely some big bloke will get out of their car and kick the crap out of me
, after all if someone can try to kill me just because he couldn't get in front of me at a turn right filter anythings possible