They're attributed to 9% of MVA deaths, and 16% of MVA injuries as of 2016, though trends seem relatively flat (or declining) since 2010.

Overall accident instances tend to scale with miles driven, which are a pro-cyclical economic factor. That is: as economic activity increases, people drive more, for both commuting and recreation.

https://www.cdc.gov/motorvehiclesafety/distracted_driving/in...

https://crashstats.nhtsa.dot.gov/#/