I have put my phone covering part of the speedometer and gas gauge when I need to see the directions. In terms of the rear view mirrors, you must have any two of the three. A work van with no rear windows had the mirror and it was kind of pointless, and sometimes hauling stuff in a car renders that mirror useless as well.

https://app.leg.wa.gov/rcw/default.aspx?cite=46.37.400