dipped my new phone (s9) a few times in the water at the pool, everything worked fine. The bottom speaker was sounding really bad and off so I cleaned it out, played some loud music and shook the phone a little bit with the speaker facing downward. after about an hour or two, the speaker was back to normal! at first I was upset but I just had to be patient ((: it's an amazing phone
So the testing that all phone manufacturers use when becoming IP68 water 'resistant' certified, is fresh water. Fresh water only.
So if you submerge your phone into chlorinated (a pool/hot tub), salt (ocean), or any other water that is not absolutely fresh water. Damage will occur.
This is why no phone manufacturer (Samsung included) do not cover water damage on their phones.
I would recommend putting your phone in a case that covers all of the open ports (when not in use) and if you want to use your phone in or near any water, put the phone in a fully water proof case or a water proof bag.
They can both be had on amazon for very cheap (I just bought 2 water proof bag enclosures for $8 with next day shipping).
I also buy all of my cases off of amazon as they are much higher quality, backed by better warranties, and the prices are much lower. Think better than an otterbox level of protection, but backed by a lifetime warranty and cost only $20 with free next day shipping.