I leave my phone in my coat pocket. Or I turn it off. Loading film into tanks only takes a few minutes. Even sheet film in trays doesn't take that long. The light from a phone can very easily fog film.

Then there's the time I forgot to turn off noise canceling on my headphones. All of a sudden I see blue light in the dark. (The headphones have a blue diode to remind that the canceling is on.) My sheet of 8 x 10 was slightly, but evenly fogged.