I literally see this happen almost every time I'm at a stop light. Someone in the queue is looking at their phone and by the time they react only a handful of cars have gotten through a light that's normally timed to move them all. Multiply this by hundreds of intersections and the effect leads to rising travel times and frustration across the board. I've also noticed a large uptick in people running stale yellow lights/newly red lights, I believe this behavior is precipitated by the red light texting crowd.

What should possibly need your attention when stopped at a red light?

If it's something frivolous then it can wait. If it's important then are you really able to compartmentalize it? Will you be able to put the conversation out of your mind, or ghost your chat partner as soon as traffic starts moving?

Are you saying people shouldn't be driving if they have something on their mind or a passenger they're chatting with?

Interestingly, chatting with a physical passenger in the car is an entirely different level of distraction, from trying to chat with someone you can't see on the other end of the phone. For some reason (invoking visual synthesis to imagine how they are responding?) the phone case takes quite a bit more mental effort.

Try putting 'blinders' on when talking to a passenger and driving normally. E.g. put a hand up so you can't see them, even out of the corner of your eye. This A/B test (for me anyway) ups the mental effort 2X or more.