It's never wise to compromise on waterproof IP rating. When you're swimming, don't assume your iPhone can handle the time and depth you're exploring. The iPhone 15 series has a rating of IP68 under IEC standard 60529 (maximum depth of 6 meters up to 30 minutes) but the iPhone 11 and 12 series can only handle 4 meters for up to 30 minutes, and older phones are even weaker.