@antonyj Indeed, do not download the Anbox image on the Nexus 5. It is already pre-installed by default. Doing so might creating bugs.

Just start here:
sudo mount -o rw,remount /
sudo apt update
sudo apt install anbox-ubuntu-touch android-tools-adb
anbox-tool install
exit

If you have an error message telling you an insufficient memory in /var, you can try as following:

sudo mount -o rw,remount /
sudo rm -r /var/cache/apt # delete the apt cache; frees space on system image
sudo tune2fs -m 0 /dev/loop0 # space reserved exclusively for root user on system image set to zero
sudo apt update # recreate apt cache to install Anbox and adb
sudo apt install anbox-ubuntu-touch android-tools-adb
sudo mount -o ro,remount /
exit