1-
Install Flatpak for Ubuntu, Debian or other Linux distributions :
https://flatpak.org/setup
2-
install Linphone by opening a terminal CTRL + ALT + T
flatpak --user install --from https://linphone.org/flatpak/linphone.flatpakref
If you install it in SYSTEM, it will probably NOT work. (I experienced it on Ubuntu 18.04 LTS)
3-
sudo apt install libcanberra-gtk-module libcanberra-gtk3-module
4-
sudo apt-get install --reinstall libcanberra-gtk-module
5-
sudo apt-get install libcanberra-gtk-module:i386
6-
Launch the app through the Menu (I’m using Gnome but it must work on Mate, KDE …)