@Lakotaubp

SOLVED!

It turns out that the post you linked was the ticket: one of the responses said that he had used a VM installation and that when he arrived at the same point I had, it was a simple matter of reconnecting the device. I had initially not investigated this solution because I had tried reconnecting many times, but I decided to give it a try because everything else had not worked, and it seems to have worked. My device is currently displaying "Installing update" with the UBPorts mascot and an orange dot indicating it is doing some work. I will be leaving it like that overnight just to ensure I do not bork any important operations.

For posterity, I will include a step-by-step description of what I did in case anyone else has this problem in the future. I feel pretty stupid right now, but I'm just so glad to have it working properly:

• Do the steps I described in my first post
• Get to the point in the GUI installer where it boots the device out of the Android bootloader and into the UBPorts Recovery mode (with the UBPorts mascot on the top right)
• You should have received a message from your Windows host machine that the device is unrecognizable. This does NOT mean you cannot connect it.
• Disconnect and reconnect the device to the Windows machine. If you have properly installed adb and the other preliminary files, then you should be able to connect it to the VM. In my case, I received a prompt from the VM because it recognized a device being connected.
• At this point, the GUI installer should recognize the device and its state, and begin downloading files.
• I did not experience any other issues to the end of the installation, and my device is now operational.

Thank you so much for your help, everyone. Now I just need to do this a couple more times so I have backup phones and I'll be set to check out of the Google/Apple mobile ecosystem.

@UniSuperBox
Thank you for your encouragement. I just checked the thread now and for whatever reason it hadn't occurred to me that the installer would be able to recover from a partial installation. I did what you suggested (connected the device to my Windows machine, then connected it to the Ubuntu VM and ran the installer from the terminal), and it detected the device correctly.

Then the following happened:

• terminal displayed some messages

info: Welcome to the UBports Installer version 0.2.6-beta!
info: hammerhead selected
info: Instructing manual reboot
info: Press and hold the volume down and power buttons until the phone reboots.
info: fastboot: wait for device
info: Download complete
info: Flashing images...
info: Booting into recovery image...
info: bootstrap done: rebooting automatically

• the device rebooted into UBports Recovery mode
• the device disconnected from my Windows machine and the Ubuntu VM, and does not appear in the Player > Removable Devices menu
• UBPorts installer currently says "Waiting for device to enter recovery mode . . ." > "Flashing recovery and boot images"

I think this is where I had disconnected it during the first installation because nothing appeared to be happening and the device seems to have disconnected. I will keep it connected now, because it's not as though I have anything else to do with it. I read a few other forum posts from people in similar situations, and one thing a couple of them had said was that the process of actually installing and booting the Ubuntu Touch files can take a very long time.

If it works itself out, I will update the thread. In the meantime, ask away if anyone has any questions.

UPDATE: I ran adb devices and sudo adb devices to confirm whether or not the VM sees the device attached, and both command return an empty list of devices. I think the installation process is frozen now, but I am unsure what to do. Logically, it seems like I should reboot the device in the UBports Recovery menu, but I am not sure if that would snarl things further.