Jeff talked about smurfing in the discord he did with the pros:
As a base rule, it [alt/smurf account] isn’t always bad. What’s bad and infuriating is boosting, throwing and generally trying to manipulate matchmaking in some way. We hate that. We have lots of focus and attention on that. Some things I can’t mention or they wouldn’t be effective but it’s an area where we really want to get better at detection and action. I’m a big fan of phone verification. It doesn’t 100% solve problems but It helps a lot. I always push for more. There are some issues and some players feel slighted by it. Also console rules add complexity to the smurfing issue.