Just touch the 3 dots in the upper right while in a call.
Wow! I wonder if AT&T version had it removed then? I tried looking for it during a call and while dialing up. Nada.. :-(
I am on ATT, it's there, once the call connects, the 3 dot menu is in the top right. It won't show until the call connects, try calling your voicemail.
I made 2 different calls just now. When the call connects and I press the 3 dot menu at the top right, I only get 3 options: Hold, View Contact and Send Message. I don't see the option for extra volume for the earpiece nor the speaker phone. :-(
This is what I get when in a call.
Strange, I'm an AT&T user as well, so I thought I would check to see if I had this feature, so when my wife called me earlier, I checked the 3 dot menu and didn't have an Extra Volume option. However, I just tried calling my voicemail, and when I clicked it then, the "Turn on extra volume" was there. Only difference I can figure out was I initiated the call to my voicemail, while the other one was one I received, not sure if that would make a difference or not.