Is he taking showers with the phone in the bathroom? Taking it swimming with him?
It's water-resistant (meaning if it gets wet, water probably won't get in. Steam gets in. Moving it around in a few feet of water can let water in), not waterproof.
1.5m of water is about 2.25 pounds of water pressure. Plunging the phone into 6" of water exceeds that. Placing it gently into a foot of water won't.
Tell him to consider the water-resistant rating to be insurance, not a waterproof guaranty.
At least, if it was steam from a shower, that's almost pure water, so drying the phone should leave it in fairly good condition (but tell him to leave it turned off for a few days in silica gel or dry uncooked rice).