I have the same problem. My iPhone 7 Plus updated to the 11.4 1 during the night and when I woke up and tried to use my headphones I just used for the gym, it didn’t work. I use them while at work and it just wasn’t even registering my headphones. Bluetooth was fine in the car, but I didn’t have any calls, just used music. But when I tried to call my husband, the speaker, FaceTime, and add call buttons wouldn’t work because they were greyed out. He couldn’t hear me and I couldn’t hear him, but I’ve been playing music all day through speaker. Siri won’t work either. I want to go back to an earlier version but I can’t even find it under the iPhone storage settings like I did before when one of my updates didn’t download right. I have so much to try to back up (128g phone) so I’d like to fix this without getting a new phone... but is that my only option?