Plug in your phone via a USB cable. Most likely, it won't appear in /run/media like a normal USB drive because the phone doesn't want to expose the full range of storage transactions which are normally available for such a device. Put another way, it wants to expose files, not blocks.
You'll see the name of the phone in left column of Files (the Solus file explorer). It might contain a vendor name (like "LG") or a provider name (like "AT&T"). If it's the latter, you may need to eject it (by clicking the eject icon in the left pane which appears next to its name) first in order to get the former to suddenly appear. (Why not just expose both simultaneously? Who knows. Probably because the device wants the OS to mistake the device for a DVD containing an install disk, so it can install crapware.)
Now go to the folder containing what you want. (DCIM is typically the folder name for photos, for unfortunate historical reasons.) In the case of DCIM, you may find other unintuitively named folders inside it. Keep clicking until you find actual image files (JPG or JPEG, typically). Select all of them, or select the parent folder, and copy (Ctrl+C). Now select a target folder, probably also from the left pane, and paste (Ctrl+V).
Now you'll discover the first bug, which is that if you have more than 50 or so images, the entire copy process will halt at like 5% progress. Sometimes if you wait several minutes, you can unplug the phone without first ejecting it through Files, and you'll find that the photos copied anyway. Sometimes you're just screwed and need to first copy them to a USB stick via some other OS.
But let's say that you do in fact manage to eject the phone properly. In this case, until you reboot, the name of the phone will remain there anyway. So the next time you copy more photos, you'll get another instance of the name. This means that if you have an XYZ phone, then you'll build up a huge list of "XYZ XYZ XYZ XYZ..." in the left pane. This is a bug that might never be fixed, so be aware of it. You can reset this list by restarting your computer, or perhaps by doing some awkward Linux workaround which I don't know.
By the way, when the list of defunct XYZ instances starts to build up, you'll never know where the "real" XYZ is. So you need to click on each of them until you find the one that contains your phone.
That's it. Eventually, you'll find a way to copy your photos. I always did.