How do I mount my Android phone?

Android doesn't support mounting your phone as a USB mass storage device anymore as of Android 4.x. It's all MTP now. Installing mtp-tools should make lsusb list your device. To mount your device as a drive you have to follow a few more steps. Check this site: http://www.mysolutions.it/mounting-your-mtp-androids-sd-card-on-ubuntu/

... but that doesn't solve the mystery of your thumb drive not appearing anymore...

If this were me I would try:

• Restarting the phone. Sometimes a power cycle is all it takes.

• A different cable. They're surprisingly fragile things with no internal redundancy. Mass production has done nothing to enhance their longevity. Most people have about a thousand of these cluttering up their houses so it should be a simple swap.

• A different port. They can break and internal connectors can fall out.

• A different computer (assuming one is conveniently close by). I once had a problem with a USB chipset that refused to talk to a SGS2 in download mode. Everything else was fine but the SGS2 would just make the USB subsystem hang. Tried it in a laptop and it just worked.

Android 7.1.x onwards (I think, but could be from 6.x also), the USB-cable connected to the device is put into charging-mode-only. This is to avoid filesystems crashing when disconnected without proper unmounting. You must switch to file sharing mode on your phone to transfer files.

After connecting your phone to your computer, go to your phone's settings and search for "usb" or "cable" and look for the option that says "Enable File Transfer" (or something to that effect). Then, the phone will declare itself as a USB device and lsusb in Linux will show the device. Then, you install the ADB Linux toolkit (using apt install <blah> on Ubuntu/Debian or dnf install <blah> on Fedora) and you can then use: adb shell your-linux-shell-cmd-here.