Theoretically, the cap space is for a point guard, and then extending Holmes and Oubre. Technically you can go over the cap if need be when signing your own free agents. Waiving and stretching Anderson (or trading him, if it were possible) would theoretically allow the Suns to address the PF issue too.
I think Booker, Warren, Ayton, Bridges, Melton, Okobo, Jackson, and Anderson are the only players under contract next summer. Oubre has a decent cap hold and Homes has a minimal cap hold. Anderson can be waived and stretched. I believe Jackson can be let go, but I am not 100% sure. They may have already picked up that option, BUT he can be an expiring contract that should be easy to trade.
My guess is that they sign and overpay someone like Rubio or Collison, and then try to grab someone like Mirotic or Randle while getting rid of one of the wings and waiving/ stretching Anderson.
Guards:
Rubio (or Collison)
Booker
Melton
Okobo
Wings:
Oubre
Bridges
Jackson
Warren
Bigs:
Ayton
Randle (or Mirotic)
Holmes
Obviously, PG and PF signings will be overpaid to get them o agree to come to Phoenix.
If they get a PF, they will really need to get rid of one of the wings. This should be pretty easy- Jackson will be an expiring contract with some potential, Warren has a friendly contract, and they can even just let Oubre go (my least preferred option.)
At that point, it's a gamble- you have competent PG and PF rotations without acquiring a star. Then you hope that Booker turns into an even better scorer, that Ayton gets to an All-Star level, and that Bridges and one other wing turn into elite 3 and D players. You are also gambling that Melton and/or Okobo will turn into a starter-quality players relatively soon. Theoretically, you have more than enough defense, more than enough scoring, enough shooting, enough rebounding.