nope, there is no such folder in /run/user/1000/.
In dolphin, the address shown (when pressing Ctrl+L) is mtp:/GM1901/Internal shared storage/. If I open the terminal from there (F4 or Shift+F4) I end up in ~.
I confirm - the device is accessible in Dolphin, go to the root of the Phone’s file system or to anywhere,
to the DCIM folder, for example, where the camera’s pictures are,
and F4 will simply open in $HOME
I can’t figure out a way to get a location in the file system.
I usually use mc instead of Dolphin - using it, I can’t access the phones storage anywhere while I can do that in Dolphin.
(I had too much time on my hands and was curious, so I checked in a Manjaro KDE/Plasma Virtual Machine to which I passed the USB device …
since I do not use Plasma/KDE I will not pursue this further)