Agreed it was technically his/her fault, but to say he/she DESERVES to get punished for this is ridiculous, so what, she accidentally left her phone in her pocket, it's not as if she was going to whip it out on the desk and start looking up answers on the Internet. If the examiners have any sort of common sense they'll know that these things happen regularly and that its just through carelessness. Honestly I think you will be fine, if your phone just went off in your pocket and you handed your phone over straight away, how can they possibly claim you were cheating? It's obviously just an honest mistake, whether you technically broke some rules or not.