I’ve enabled developer mode and can SSH into my phone. On my Kubuntu laptop I can use SSHFS to mount the phone to a mount point, and use the Dolphon GUI file browser to see the files on my phone in /home/defaultuser. So I have no problem copying files from here to my laptop, very nice, better than anything I’ve ever managed with an Android phone.
But how do I access the phone’s SD card? (To copy my photos to my laptop).
It is there:
sftp://defaultuser@192.168.0.1/run/media/defaultuser/0123-4567
You can make a symlink of this directory in your home folder to have it easier in the future.
Instead of 192.168.0.1 in my case, type the adress your phone has. You can read this adress in Settings/developer tools . If your phone is also your internet router/WLAN access point, it is 1 like mine in the example above.
edit: I use the built in SFTP of Ubuntu/Cinnamon Desktop, this creates also a desktop icon for the phone’s file system.
You can also use FileZilla for access.
That worked great, thank you!
No need to do anything with sshfs, and I can add the phone and SD card sftp: as a “Place” in Dolphin, it remembers the password, all I have to do is click on it, all very convenient! (Except the huge SD card mount point hex number is not so convenient to type, shame it could not just be just /run/media/defaultuser/sdcard or something!).
This ‘0123-4567’ is my SD cards name out of the box. Maybe rename your SD card and check if ‘0123-4567’ (in my case), or your SD card’s long number, changes into a pretty name, like MemoryCard or something you want.
You got off lightly… mine is 6e3ca163-540d-4df7-8bec-44b0291293a7 
Yes, thats no fun to type this. Can you rename the SIM card using computer, and give it a shorter name?
Bookmark the sd card in FileZilla. Easy as can be. 
It already has a label but clearly is not being mounted using that name (unlike on my computer, which does).
The long number is the UUID - I guess created when I formatted it? Anyway my laptop does not allow me to change it 
and I am not in the mood to reformat it just to see if I get the option to choose the number!
I can live with it - my laptop has remembered it and the password, so my photos are just one click away. 