A contentious issue that has been debated for the last 25 years I've been in my Food Safety Compliance roll. As the years have past, electronics miniaturized and cell phone ownership/usage so has the call become louder more prevalent so has the perceived justification for it's inclusion. Yes, we've all been confronted with the usual emergencies, breakdown etc. and have had to evolve our GMP policies to recant any reason that these electronic items are generally permissible inclusions within food production facilities.
I too have management who have evolved into technomaniacs, were the little devices they worship every day, must be attended to immediately, every time they beep, vibrate or ring instinct tells them they must attend to whoever/whatever the person at the other end has contacted them about. Don't tell me that a phone in a persons pocket is going to remain there if it activates and once attended to the person is going to comply with all the policies before returning to their task. IT'S NOT GOING TO HAPPEN.
I like other's in this Topic String have had to make it quite clear with policies, training and GMP audit violations that this practice is not permissible, but there are documented limited exceptions, as eluded to by others here.
Initially my risk assessment focused on the glass aspect of the issue but as ownership/usage ramped up my focus moved to contamination. The use of these in the toilet and the total lack of sterilization of the equipment makes the risk of inclusion into the production area as high as not washing your hands after going to the toilet. Ask those that are opposing the restriction if they'll relent on that policy and see where it leads you.
I googled "how clean are mobile phones" and this was the result: About 70,700,000 results (0.51 seconds) and I bet none of those shows a positive result.
I picked just 2 on the first 5 to pop up that would lead to any right minded, committed food safety organisation to ban the practice.