I carry 2 iPhones daily, an iPhone 14 Pro Max for personal use and an iPhone 12 provided by my work. I recently upgraded both devices to iOS 17.
Ever since the upgrade, whenever I stack both phones together either on my desk or in my pocket, I get an "iPhone Connected" black banner on the top of each phone. The banner isn't easy to swipe away or close and it doesn't provide any context on why it's there. It also hangs around in the Dynamic Island on my 14 Pro Max. I've been doing some searching on this for weeks and finally came across this post today that solved the issue:
https://discussions.apple.com/thread/255157985
Apparently this is because of the new AirDrop feature that allows for starting AirDrop sharing by bringing 2 devices together. You would never see this banner unless you stack your phone on top of another iPhone, so having 2 iPhones made me encounter this issue more often.
This can be disabled by going to Settings > General > AirDrop > and turn off Start Sharing By Bringing Devices Together
Once I turned that setting off the issue is resolved and the banners are no longer displaying.