A safe way to run Linux on your smartphone or tablet is to take advantage of VNC viewer. Then on a raspberry pi computer running Ubuntu MATE you could run vncserver. The reason for the raspberry pi computer is safety. No need to run a vncserver on your main machine.
I wanted to preserve battery so I thought I connect the raspberry pi with the smartphone by the USB cable. This can actually be done using USB-tethering. The whole setup is mobile with a powerbank for the Pi.
Its not hard to do the setup but it requires too many steps I think. Maybe we need some easy way to do this on the Raspberry pi?
Actually it was much more fun running Linux fully portable using Wifi.
Updated with a video