Nice thought, and it would be nice if it worked that way.
Do the insurance companies care? Kinda seems like their rates are based on the claims paid, but I have to admit that I do not understand how the business works.
I don't think insurance companies even have access to mobile phone records.
And if they did, and denied a claim based on a phone being in use, how do they prove that the driver was the one using the phone? In some other thread long ago, I remember seeing something like "No I didn't call you. My butt called you" -- must have had something to do with somebody sitting on their phone. So just because a phone was active, that does not mean the driver was using it.
Additionally, you just don't seem to hear about claims being denied based on the insured doing something they should not have done. That kind of goes against the idea of mutual protection. Maybe they will not be renewed, but the claims get paid.