Strange, I have not had this issue yet with the earpiece volume. In fact, it is a bit too loud even at 75%. The external speakerphone is ridiculously loud as well.
Not only do I have that issue, but I WS putting it on speakerphone to solve the problem and now I am having to hold the speaker up to my ear at times to hear what is being said. The sound is clear and loud on my Bluetooth speaker. I hate Bluetooth headsets, so that is simply not an option.