Multiple small pieces of reflective material moving fluidly like a flock of birds high in the sky

Driving north on highway 285, a reflection of sunlight caught my eye, except it was coming from the north instead of the direction of the sun. I looked up and saw a very unfamiliar sight. The reflection was coming from what sort of looked like a flock of birds similar to how starlings could move (fluid but creating beautiful patterns while flying roughly in the same area). So I first thought they must be some sort of bird flock that looks very white and could possibly reflect sunlight, but I’m not sure of any birds that fit that description and this was very high in the sky. I continued to watch it move around and continued on. Two other things to note, cell service dropped off right before I saw the thing and there were other cars there, just traveling south. When I looked back in my mirror, I could not see the thing anymore. The observer is a college graduate with no history of observing anything like this and is aware of how crazy this sounds.