From the original FlightAware track they had been as high as 7800' and then were descending. I suspect he might have been between layers and was trying to stay VMC.
I still wonder about icing in this situation. I am a new instrument rated pilot and so am looking for safe IMC to practice in. That very morning I had considered a flight north from Phoenix but was worried the freezing levels were too low for my Cardinal.
In this crash the pilot descended and accelerated, going straight, prior to impact. And it appears the plane broke up in flight from the photos.