The Suns are so predictable that it's easy to prepare against them. You already know they can't do shyt on defense so you make it difficult for them to score or get in a rhythm. Nurkic the only real big man they have and while he's preformed well you still need reinforcements and the Suns don't have that.
Booker isn't a playoff performer, Beal is spotty and unpredictable on offense and KD the only guaranteed bucket on the court while the rest of their bench ain't producing consistently.
I do think Phoenix will regroup and come out better in game 2 with the proper adjustments.