At https://www.androidauthority.com/block-phone-number-android-246484/ I see:-
"Block a phone number on Android by opening your Phone app and going to Recents. Tap and hold on to the number you want to block and select Block/report spam."
When I do that the Block/report spam option does not appear. Once I go into the phone app, select recents and tap a recent call, it shows 1 selected. An All button shows, also search "magnifying glass" and a delete icon, there is no block or menu option.
The unwanted phone number is not in my Contacts list, so that alternative is not available.
I run Android 13 on a Samsung Galaxy S20 FE 5G.
So how do I block the number?
Don't tap and hold, just tap on the phone number, press the (i) and then I can see a 'block' button at the bottom.
If you google how to block phone numbers on Samsung phones, you'll get better results than generic android phones. Samsung has its own phone/contact app and has slight variation to the stock android.