Under water usage

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

Do not, take your iPhone under water. It is not water proof. It will be damaged if you do.

You need a pressure rated, water proof case to use an iPhone or iPad under water. True underwater cameras and camera housings are not rated for simple water resistance. They are pressure rated to withstand a particular depth and pressure of water.

All a water resistance rating means is that your device is less likely to be damaged from splashes or short term water exposure than a non-resistant device would be. An IP67 or 68 rating is not an endorsement to use a device as if it was designed for deliberate submerged use.

Do not submerge your phone in water. It is not waterproof. The reference to being under water was done in a controlled situation only.

Your phone is NOT waterproof. Do NOT use it for taking pictures underwater. If you do, you will destroy it and it will not be covered by warranty.

Don't do it.

iPhones are not waterproof.

If you want to use your phone underwater, you should get a waterproof case which you must validate is waterproof before using your phone under the water so you know it doesn't leak. Otherwise, what all the others have said is definitely true