True that but even the petrol pump employees use their own mobile phones.
The smartphones these days are better built than the feature phones of yesteryear. This safety rule was made when we had nokias and other samsung phones of inferior quality which could create a spark. And the iphones and androids had not come to India.
Even the swipe machines pose a hazard as they use either an electric adapter or a battery. They are also in the category of mobile phones as they have the gsm chip with GPRS facility.
So, this safety feature is somewhat obsolete. But this is just my opinion.