Those who claim that it will cause problems are most likely referring to the sensitive components in phones that are sensitive to heat, as well as humidity and sweat.

The fact that a cell phone is waterproof does not imply that it is heatproof.

The damage is still present, even if it is not immediately visible due to the nature of the damage. Heat and electronics simply do not mix, and the device's battery and other electronic components will suffer long-term consequences as a result.
When using an iPhone in the sauna, is it safe to do so?

When it comes to questions of this nature, this is one of the most frequently asked questions. If you're looking for a short answer, iPhones are no different than other phones when it comes to heat damage. The optimal temperature range for iPhone use is 62° to 72° F (16° to 22° C). Apple also warns that exposing your iPhone to temperatures above 95° F (35° C) will permanently damage the battery capacity of your iPhone.

And don't even think about putting a battery in there to charge it! The consequences of plugging in your phone while it's hot are even worse than using it. Even merely storing it in a hot environment can result in long-term degradation.

Tips for preventing your phone from overheating while in the sauna

In the event that you absolutely must bring your phone into the What Kind of Home Sauna to Purchase with you, proceed with extreme caution. Here are some suggestions for reducing the likelihood of your phone overheating while in the sauna:

Stay near the entrance, where it's a little cooler and more ventilated, for the best experience. Not only will this reduce the amount of heat generated by the phone, but it will also allow it to wick away more moisture.

Keep it to a minimum. The less time your phone spends in the sauna, the less heat it will absorb from the environment. Allowing the phone to cool after exiting the sauna after a brief session is recommended before entering again.

Use a protective case with extra waterproofing capabilities, wrap it in a towel to insulate it and protect it from heat and humidity, and wipe any moisture that accumulates on its surface on a regular basis with the towel.