For $99. If you are already paying for normal MLB.tv, you would just have to upgrade to the DBacks TV + MLB.tv for $199 total (no idea how that works if you get MLB.tv through T-Mobile). That would be the legal way to watch Dodger vs DBacks games in Utah.
I think the games might also be on DirecTV and DirecTV Stream and Fubo in Utah, although someone would have to verify. So a few options.
The DBacks TV thing is the future though. Eventually the idea is you’ll be able to pay for in-market and out-of-market MLB.tv.