1. Devin Booker
The nuclear option, but we all know that Booker is the most valuable trade asset that the organization has. There is obviously zero indication that the team would be willing to move him - that New York Knicks chatter once they were eliminated from the playoffs was never serious - but that doesn't change the fact he'd fetch the Suns the most in return.
Like Durant, it would also help ease the strain of paying three players max contracts, although a move such as that one would just be a repeat of the cost-cutting decisions of the Robert Sarver era. If Durant is somebody you quietly consider moving and Beal is somebody you gladly would if he didn't have a no-trade clause, then Booker is the one who remains off limits.
Obviously if he expressed any desire to leave that would change the situation completely, which is why this is something that won't be entertained unless the unthinkable were to happen and Booker asked out. Trading him would also reroute the franchise in a completely different direction, one which would include moving Durant as well.
If the Suns wanted to a war chest of first round picks and a budding star plus some other stuff though, Booker would be the only way to get that done. That no other player on this roster comes close to achieving this for them tells you all you need to know about where they are currently at, and it is why Booker will top this list as long as he is in Phoenix.