As others have said, yes, this is the only formal interview for UA - Phoenix.
Your VITA responses will go to all participating schools that choose to interview you, so unless UA - Phx is your only school utilizing it, try and keep your answers from being school specific.
The VITA isn't too bad. The best advice I have seen and what I would pass on is this:
1) Do the practice VITA -- it gives a great sense of the types of questions, the timing, etc.
2) Review the 5 competencies, and have a handful of anecdotes on hand that you could potentially use to illustrate how you are proficient in these areas. Personally, I tried to pick 2-3 scenarios that I could double dip depending on the angle/info I wanted to provide.
3) Look at strategies for responding to situational judgement questions. I found a reddit thread about the CASPer test that had a guide on the different steps in answering ethical and hypothetical situations. Basically its: (1) Acknowledge the situation, (2) Explain your understanding of the 2+ perspectives, (3) Describe your role in the situation, (4) Explain your decision, and (5) Justify your decision.
Hope that helps!