That's not relevant. Your phone does not need to work for a long time underwater. The phone can be perfectly waterproof even if there's water between phone and battery.
My phone is a lot more sensitive to water intrusion. Having dropped totally non-waterproof flashlights in pools as a kid they'll generally still work even if totally flooded. Even if they get bad enough to stop working they'll almost certainly work perfectly once dried out.
That's not the case with a modern smartphone.