USB Android phone direct mount

I have previously mounted my HTC U11 directly with MP3tag via USB using VirtualBox on a Mac Host.
The phone is showing as drive G, but MP3tag can't mount it.
What have I forgotten?
Thanks,

see here:

pretty sure now that I was wrong.
I think I accessed the mSD directly on a sled.
I've gone through a bunch of trouble shooting with both VirtualBox that I'm running W7 on and MP3tag.
Drivers and HTC sync software.
Nothing better. I think it's a VB issue.
I've gone back to the mSD in sled.
It's reading the directory now.
Should be fine.
Thanks for the leads though.