Installare flatpak:

sudo apt install flatpak

installare linphone e le dipendenze

flatpak --user install --from https://linphone.org/flatpak/linphone.flatpakref

creare il file desktop con 

sudo nano /usr/share/applications/linphone.desktop

ed inserire il seguente contenuto:

Comment=
Terminal=false
Name=Linphone
Exec=flatpak run com.belledonnecommunications.linphone
Type=Application
Icon=~/.local/share/flatpak/app/com.belledonnecommunications.linphone/current/active/files/share/icons/hicolor/scalable/apps/com.belledonnecommunications.linphone.svg
Name[en_GB]=Linphone

Aprite Linphone dal menu applicazioni

Enjoy! :)