How water-resistant is the iPhone, really? Some iPhones  were advertised as being "water resistant" so I thought that there was no problem with keeping them in the bathroom out of the bathtub so that I could listen to music. Will they be safe?

After all, if you can submerge an iPhone under liquid water for 30 minutes, then water vapor, which is filled with similar sized water molecules while having much lower density of water (and hence the minerals that come with the water) should be of no concern. Am I wrong?
Apple's technical support document suggests avoiding taking an iPhone into a steam room:


  About splash, water, and dust resistance of iPhone 7 and later
  
  Learn about splash, water, and dust resistance on your iPhone. And learn what to do if your iPhone gets wet accidentally.
  
  ...
  
  To prevent liquid damage, avoid these:
  
  
  Swimming or bathing with your iPhone
  Exposing your iPhone to pressurized water or high velocity water, such as when showering, water skiing, wake boarding, surfing, jet skiing, and so on
  Using your iPhone in a sauna or steam room
  Intentionally submerging your iPhone in water
  ...
  


Strictly speaking, iPhone 8/8 Plus/XR are rated as IP67, later models as IP68. See Wikipedia for details, Apple claims 30 minutes at a depth of 1 meter for IP67, 30 minutes at a depth of 4 meters for IP68.