Fab - all done! With lots of help from the lovely people on the UBports supergroup on Telegram

Firstly I downloaded to my computer the recovery image file for Meizu MX4 from: https://wiki.ubuntu.com/Touch/Devices#Working_with_ubuntu-device-flash

I needed to do this because it is a retail phone that shipped with Ubuntu installed already (and is currently running Ubuntu).

I rebooted into FASTBOOT (the bootloader) by pressing down on the volume button and power button at the same time and holding it until I could see =>FASTBOOT on the phone screen.

In the terminal on my computer I typed in: ubuntu-device-flash --server https://system-image.ubports.com touch --recovery-image recovery.img --channel ubports-touch/15.04/stable --bootstrap. If you have a different file name for the recovery image file you would need to put in a different file name where I've put recovery.img

On my phone I could then see a purple background and ubuntu logo. In the terminal window I could see a terminal output showing that it is pushing files.

Eventually the terminal output read "Rebooting into recovery to flash". The phone then reflashed and installed ... with me watching

Meizu MX4 magic-device-tool - I think I've done something wrong ... I'm stuck in a loop