some sort of plastic or rubber is degrading, maybe my phone case?

There’s this type of coating – I commented on it a while back, will link to my comment in a sec – that was put on a lot of consumer electronics that over time, breaks down to become sticky.

kagis

lemmy.world/comment/12199022

TPE, thermoplastic elastomers. They break down over time into really sticky goo.

I haven’t seen it in some years – was a real problem maybe, I dunno, ten years ago? If your thing is only six years old, I dunno if it’s that.

But isopropyl alcohol and enough elbow grease will get it off, if it’s just a coating on plastic.

I don’t see anything when searching for “sticky otterbox”, though, so I don’t know if that’s the factor, even if that’s what’s going on here. My experience that the source is pretty obvious, since it’s a “grippy” rubberized thing that becomes sticky.