Is my iPhone water resistant?

See this, About splash, water, and dust resistance of iPhone 7 and later - Apple Support and this statement contained in it.

Splash, water, and dust resistance are not permanent conditions and resistance might decrease as a result of normal wear. 

It isn't permanent. Contact Apple Support with any questions. Use the Get Support link at the top of the page.

iPhone's have a degree of water resistance, but they are not entirely water proof. There's a difference.

You cannot submerge the iPhones and expect them to continue working.

See here: link-> About splash, water, and dust resistance of iPhone 7 and later - Apple Support

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
• Operating your iPhone outside the suggested temperature ranges or in extremely humid conditions
• Dropping your iPhone or subjecting it to other impacts
• Disassembling your iPhone, including removing screws

"Water resistant" is not the same thing as "water proof"