I personally like to put it in the negative.

Let's set aside for a moment FAA, FCC, IATA, etc.

The airline has a several million dollars/euro worth aircraft to lose in case of a crash.

The insurance has many more millions to pay.

If I were them and if I suspected that having phones or smartphones switched on and/or used during flight might in 0.00001% of cases cause a crash, my policy would be to frisk all passengers and take all their electronic devices in custody before boarding.

Since this is not done, they (airline and insurance) must be pretty sure that the devices (and their use) are not dangerous for flight safety.