The second half of SLFguy's first post makes a lot of sense.
Static electricity CAN cause gas explosions, and has done so often enough.
Anybody who's got out of a car on a hot and dry day, and got a nasty jolt, will be aware of that.
Sparks inside cell phones sound unlikely, they wouldn't keep functioning for very long....
But the scenario is easy to imagine..... start refuelling, then the cell phone rings. You slide back into the car, answer the phone, slide back out (nicely charged with static electricity), get to the back to remove the refuelling hose... and BOOM.
Not everybody is capable of discerning cause and effect, so the cell phone getting blamed doesn't astonish me one bit.
In practice, I can't really see any way to ignite gas vapor with a cell phone. Voltages, currents, temperatures and emitted power all seem to be far too low.
With static electricity... NO PROBLEM.