KDE Connect is a built-in application in Kubuntu that allows integration between a Kubuntu laptop and an Android phone.
To prepare the Android phone: install KDE Connect from F-Droid or Play Store, enable WiFi and connect to a local hotspot.
To prepare the Kubuntu laptop: open KDE Connect from the system tray or start menu, select the phone name and pair it.
To test KDE Connect: on the laptop, send a file to the phone using Dolphin file explorer, or on the phone, send a file to the laptop using KDE Connect.