This implements logging of ingoing and outgoing calls to your calendar. I use an extra Nextcloud calendar “CallLog” for that purpouse.

• App Tasker (sorry no FDroid)
• App CalendarTask (sorry no FDroid)
• Additional permissions for Tasker, since Android 8:
  • android.permission.PROCESS_OUTGOING_CALLS
  • android.permission.READ_PHONE_STATE

adb shell pm grant net.dinglisch.android.taskerm android.permission.PROCESS_OUTGOING_CALLS
adb shell pm grant net.dinglisch.android.taskerm android.permission.READ_PHONE_STATE

Click this URL on your Android phone to import the project into Tasker:

Tasker Project CallLog

Alternatively here is the CallLog Project as compressed xml.

After import you have to edit the 'SubTaskLogCall2Calendar' and choose which calendar to log to.