Android Calendars

[J Wadle]

I'm using Android 7.0 on my Samsung S8+. My primary email/contacts/calendar are in my outlook.com account which I access via the Outlook app on the phone. I also sync these to my Google (gmail) account via my desktop PC. Generally, this all works.

However, I am confused about the calendars/contacts that are kept on my phone. I assume that the Android built-in Calendar app accesses my Google calendar and I have the Outlook app setup to access my outlook.com calendar. There also seems to be a third calendar on the phone - an Android calendar? - that is separate from the Google calendar.

If I add an event on the phone via the Android built-in Calendar app or Google Assistant by voice, it doesn't show up on my Google or Outlook calendars, only on the phone calendar via the built-in Calendar app.

Is there a third calendar besides Google and Outlook on the phone?

Thanks