[squarefoot]

My father's underwater flashlights from the 1970s had replaceable batteries and were quite water resistant, I mean from sea water, not just rain. Of course a phone makes it more difficult both for its shape and size, but hey, technology progressed a bit in 50 years.

[happyopossum]

And they were HUGE. With giant o-rings that wear out or need to be lubricated regularly, and would fail if they weren’t.

[jacquesm]

Underwater flashlights sooner than not suffer from outgassing and tend to have pressure relief valves and multiple o-rings to keep the water out. O-rings do need a bit of maintenance but it's not a huge burden.