This app will install Debian Buster with Xfce desktop environment.
You do not need to root your device.
You will need 1.2 Gb free on internal storage.
A mouse or stylus is highly recommended.

This app is NOT full Debian OS - it is a compatibility layer, based on PRoot, which allows you to run user-land Debian applications.
Your phone is not rooted during installation.
Running Wireshark or Aircrack-ng will fail, because they require root. 
This is not an official Debian.org release.

To install packages (web browser for example), open Terminal and run commands:

sudo apt-get update

sudo apt-get install chromium

You can check full list of packages in Synaptic package manager.

Packages that work:
synaptic gimp inkscape clementine chromium vlc mplayer audacity lmms

In VLC and Audacity, select PulseAudio as audio output.

To run Chromium, use command:

chromium --disable-dev-shm-usage --no-sandbox

Packages that fail to run:
firefox-esr libreoffice konqueror kodi kdenlive blender, and anything that uses OpenGL.

Sources are here:
https://github.com/pelya/commandergenius/tree/sdl_android/project/jni/application/xserver-debian
Previous versions are here:
https://sourceforge.net/projects/libsdl-android/files/ubuntu/

Debian noroot

Additional Information