ABSOLUTELY!
Even an IP-68 phone isn't air-proof, so it isn't steamproof. The steam will get inside the phone. Then, when the phone cools down, the steam will condense and you'll have water all over the inside of the phone - and eventually (a matter of weeks or months, depending on the dirt in the air that got into the phone). the phone will stop working - and it's not covered by the warranty - nor even by preferred service.
You shouldn't have the phone in the bathroom when you take a shower - not even on the other side of the room.
(The same thing happens when bringing a room temperature phone into a sub-freezing outdoors, or a sub-freezing phone into a warm humid space [like anywhere there's a humidifier running or a fire burning].)