Crossing a crosswalk while looking at a phone

What happens if someone is looking at their phone while crossing a crosswalk,
fails to notice a stopped vehicle,
encroaches halfway into the crosswalk,
and collides with a car waiting at a red light?
Who is at fault here?
Did the car commit a signal violation?
This is what happened to my dim-witted high school nephew during the day.
He said he was fine at the time,
but now he's complaining that his knee hurts ㅡㅡ