SlackBuildsOrg/multimedia/gmtp

A basic MTP client.

Supports MTP devices including those with multiple storage devices
(typically mobile phones). Supports Drag'n'Drop interface for
upload/download of files.

This doesn't pick up my device (Droid Ultra) as a normal user, so I
use gksu to launch it and it works great. Xfsudo works as well. It may
or may not detect your device as a normal user, I have no idea and I
make no promises.

This package is built with gtk2 but the default is gtk3,
if you would like gtk3, simply delete or comment out the line
  --with-gtk2
from within the SlackBuild script under the configure flags.

There is a FAQ inside the source tarball in the README.