I'm surprised the numbers for Phoenix are so low (10's of thousands of rides). I'm not sure if that fleet is just very small or my sense of how many rides/day a major metro can generate.
They operate in only a small area of Phoenix metro – Chandler and some parts of Tempe. That's why the numbers are small.
My guess is Chandler is purely a testing ground for them to learn to operate a robotaxi service. Things like remote assistance, customer support, emergency protocols, fleet maintenance etc.