Yup, I saw the same thing with an iPhone (not mine, for someone else) a few years ago. The person reported that the phone was heating up and misbehaving, once the Apple Store looked at it they determined it had been exposed to water. At this point, the damage is done, recovering from this is going to require opening the phone and doing cleaning that only a properly-equipped shop could do, if it will even fix it but that gives the best hope.
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