GP isn't nearly as important as matchup knowledge. If you go into the desert with a fish and expect it to do well, you're going to have a bad time.
Phoenix, as always, gets hurt by daze. The addition of Rex just made daze even better against them.
Like most teams, they don't like buff immunity, healing immunity, shock, or blind.
There are plenty of options to beat them.
They are not toxic, they just have swarm synergy which exists with many other teams (Geos, Moth Rebels, even Imp Troopers).
If you're in a position where you get this upset to a team like Phoenix, this might not be the game for you. There are far worse monsters out there (like Malgus).