As I see no 'smiley' I assume you mean that seriously.
In my view, anything that includes a battery can cause a spark. Switching off engines and onboard 'entertainment' at pumps makes sense too; I'll never forget the moment that Benetton F1 car burst into flames in the pits, though I'm willing to accept that spillage onto red-hot mechanicals probably had more to do with that event than coursing electricity...
Yes, I meant it seriously. The voltages in mobile phones, and the energy in the radio signals, simply isn't sufficient to cause sparks or to ignite fumes. There's infinitely more danger from the chap next to you starting his engine to leave.
F1 has a wide variety of dangers not commonly found outside the track / pits!