This is a known problem and is widespread and it pretty much doesn't matter what gear you have. In fact, I've heard on movie sets with location sound being recorded, it has become a HUGE problem that causes things to be re-recorded all the time. Best thing you can do is turn your phone off, and have anyone in your immediate party turn theirs off, and then cross your fingers. The more modern the phone, and particularly GSM phones, the more likely this will happen regardless of whether there is a phone call being made -- the new phones "phone home" a lot more than they did back in the day.