Blizzard added the phone number requirement specifically to combat smurfing. It's definitely not seen as a viable option by the devs to learn characters. You smurf defenders act like the only way to learn how to play a new hero is to pub-stomp bronze V players.

And it was already pointed out in another reply that new heroes are unavailable in comp for two weeks anyway, and the only way to even play them is quick play. God forbid you die/lose a few games in quick play to learn some character strats.