Courtney, I think you will find during refueling and using a phone it may be static that is the issue or simply the phone is not intrinsically safe, ll the electric devices in gas stations are protected with explosive containment devices, mobiles will not be.
I remember we used to do rotor turning refuels on Wessex whilst plugged into the intercom, however tests were carried out and it was found that there was so much static floating about because of that, the potential was there to cause a spark, hence the on intercom refuelling was forbidden after that.