Well, I would think the phone would be an important detail if it was an important detail, did it delay you making a stop longer than you had warning to make the stop regardless. Not talking like .00000000001 seconds of delay, but enough to make a difference in the events? if so, remember before saying it in a court room doing something illegal could make it your fault (which it wasn't, really, if you could go after people for actual fault, both of you should be looking at the guy who stopped abruptly in front of you). But if being on your phone made you not react and you otherwise would have not been hit, you were coincidentally on it and it played no role, if you could have not been hit if you were not on your phone, it is a cause and if you can afford to, you should say something. Only you and any passengers can recall what was happening at the time, so you would have to go through your memory and investigate if the phone was a factor.
Either way going forward you can save yourself this feeling by not using your phone while you drive, since it is causing you to feel this way, regardless of if it even mattered or not.