I just updated to iOS 12.1 this morning (11/13/2018). My phone worked just fine last night before I went to bed. When I woke up this morning, I noticed I had an update available, so I installed the update. An hour after the update, I plugged in my headphones and much to my surprise they weren't working (music was still coming from the phone). Although I was puzzled, I shrugged it off. Then about two hours later, I tried to make a phone call and notice that the call is on speakerphone automatically, with the speaker button greyed out. When the person I was calling tried to answer the phone, I could no longer hear anything and on their end the call dropped. It's not just coincidence that this happened out of nowhere!! My phone was in perfect operating condition prior to this update!!
I contacted Apple Support and they acted puzzled (which, after reading this now I see that as a bunch of BS, because they are perfectly aware of the issue). They instructed me to back my phone up and do a factory restore. So, I'm going to give it a try, although I'm not at all optimistic that it will work!