I too love a bit of music in the bath or even the news when I shave!
You really should get a Bluetooth or WiFi speaker of some sort. I started off with a UE Boom taking it in the Bathroom already playing, when it finally died I jumped to an AirPod best move I could make! Now I don't need to pre-start the music and if I need to I can switch things around without touching it! I could take the iPhone in but I really don't want to tempt fate dropping it with wet soap hands.
Well it does sound like you get some water inside around the trackpad. Here's the needed part [product|IF188-125] and the guide to put it in [guide|135507]