What do you feel would have been the right action here?
Probably ask him to pull over to text or stop but I appreciate it's hard when it is a boss and you probably felt intimated. It's illegal to be on a phone while driving where I live. I have issues with car drivers and bikers myself. I have only 3 people I will get in a car with and only one I'd ride on a bike with. People get offended but if they are dangerous drivers I won't travel with them. End of.