It is always advisable to not use mobile phones at a petrol pump. There is not a confirmed study to show the effects of using mobile phones at a petrol pump, but being cautious doesn’t harm anyone and most of the countries have prohibited the use of phones in a petrol bunk.
Source: http://thelogicalindian.com/story-feed/awareness/video-why-not-to-use-cellphones-at-a-petrol-pump/