Nextcloud Talk as a receiving client on the Pi3B+

I installed NextCloudPi on The Pi3B+ and it works so far. Though I want to call the Pi from my Androidphone and the Pi should automatically accept 2 contacts and go into fullscreen-video.
The other thing is, this should be working without needing any key or buttonpress since the Pi runs without mouse and keyboard.

Is this already intended in the webinterface or do I have to tinker? First thing I need to install is some windowmanager like LXDE and probably Chromium? This is my first try after giving up with Jitsi Meet and Google Duo on the Pi.