I have found the same true with Bluetooth and also find one ear bud not a problem.

When I had my first iPhone bar mounted it was as shown when I went to the iPhone 4 I had a otterbox case on it and the belt clip attached to just a little bracket (tab) thing I made. I also set it a little lower and less likely to get wacked. One concern I had was the phone being out in the sun for long periods of time and of course rain even in a semi protected case. With how my bar bag (re purposed camera bag) is mounted on the inside of my bars it’s really easy to flip open the top and there is the phone, the top also shades the screen some for viewing. I like your idea of a clear window in the top of my bag that might be an idea worth thinking about.

For phone calls I mostly put it on speaker.