There are warnings to not use a cellphone, but probably more to cover all bases or to prevent people from getting distracted. It's mandatory to have hoses that catch any vapours and return them to the underground storage tanks, so it's very unlikely the concentration in the open air will ever reach a point where ignition by cellphone is possible.

Also all nozzles here are designed to automatically switch off when your tank is full, even when you keep pressing the lever, so I'd say even the distraction part is pretty moot.