I usually avoid alarmist subject lines, but I believe this one to be fully justified.
Today I activated the Voiceover setting that automatically switches a call to speakers if the iPhone is removed from your ear. Then, while listening to some music at high volume over the iPhone's speakers, I received a phone call. A few minutes into the call, my iPhone switched to the lock screen, which for some reason triggered the automatic switching to speakers. As a result, the sound of the call blurted into my ear at almost full blast. To be fair, I can detect no immediate damage to my hearing after the incident, but it sure was very uncomfortable. I like to trust my device to be safe for daily use, and that trust, for me, has been temporarily violated.
The workaround, of course, is not to use the aforementioned setting.