How can I get a copy of my call log ?

Not much you can do with native options, just last 100 calls in Recents tab... Check iMazing maybe, it will show you the full log in free version, but exporting it in Excel/CSV will require a license (guide if needed).

Check with your mobile provider’s account management website or their iPhone app if they have one. It will show a complete call log going back at least 18 months.