Water proof and water resistant are two different things. I don’t recall Apple advertising that any of their phones are water proof.
From: https://support.apple.com/kb/SP779?viewlocale=en_US&locale=en_US
“iPhone XS and iPhone XS Max are splash, water, and dust resistant and were tested under controlled laboratory conditions with a rating of IP68 under IEC standard 60529 (maximum depth of 2 meters up to 30 minutes). Splash, water, and dust resistance are not permanent conditions and resistance might decrease as a result of normal wear.”
The water resistance works because of water tension; the phone will be water resistant under normal conditions, but forcing water under pressure into an opening would likely result in water entering the casing of the device.