We can block entries of dialed or received phone numbers directly in the call history of the phone app on the OnePlus smartphone, regardless of whether that number is stored or whether the calls are from supposed contest partners.

To block a phone number directly from the call list, the corresponding entry must be held and then tapped on the block button in the pop-up window displayed.

The number can also be directly marked as a spam call and sent or reported to Google.

Android 10 | OxygenOS 10.0
Block phone number (Call history) -  Open the  Phone app
Block phone number (Call history) -  Tap and hold an  entry
Block phone number (Call history) -  Tap on  Block/report spam
Block phone number (Call history) -  Confirm with  Block
  1. Open the Phone app
  2. Tap and hold an entry
  3. Tap on Block/report spam
  4. Confirm with Block

OnePlus Instructions