Ubuntu 18.04 does not connect to Android smartphone
I have the same problem with ubuntu 18.04 lts and a samsung s6 edge. When I connect the phone to my pc and open Nautilus it shows no files or folders. But I stumbled on a work around: close all instances of Nautilus, dismount the phone and turn it off without disconecting it. Then turn it on and sometimes Nautilus can see it. Hope it works for you
On the phone, you have to click on the notification that says "use this USB for charging" and change it to file transfer.