I kept getting errors about the system being unable to mount an MTP device and have resorted to some ridiculous things trying to get content off devices. Under KDE, Dolphin never seemed to work to get things via MTP (Media Transfer Protocol), but Konqueror did so I just used that. Yesterday I did a search for ‘ubuntu unable to mount nokia unable to open mtp device‘ hoping to find something that would help and I did on AskUbuntu!
sudo apt-get install mtpfs
One other thing I’ve noticed in Kubuntu is that every instance of Dolphin seems to require the Android device to ‘Allow’ access. So if you’re copying from one Dolphin window to another you’re likely to get a ton of requests. On the other hand, if I accessed the device, allowed the access, and just split the window view I was able to copy or move files from the device just fine.