KDE Connect is quite simply a program that connects your Kubuntu desktop to your Android phone allowing you to share files, notifications, ring your phone, use it as a remote or a pointer and much more. In the few years it has been out it has become an almost indispensable part of the Kubuntu desktop.
KDE connection should already be installed on your Kubuntu desktop but if for any reason it needs to be reinstalled you can do so by opening Konsole and typing,
sudo apt install kdeconnect
After installation it can be found in the system tray on the right or by searching in the main menu.