Blocking calls helps you avoid unwanted disturbances from unwanted callers.
Blocking phone numbers on Samsung Galaxy S8 Plus is done as follows:
Step 1: Navigate to the 'Phone' app.

Go to the 'Phone' app.
Step 2: Select '...'.

Choose '...'.
Step 3: Select 'Settings'.

Select 'Settings'.
Step 4: Choose 'Block numbers'.

Choose 'Block numbers'.
Step 5: Block numbers from: Unknown callers, entered numbers, contacts.

Block numbers like a ninja: Hidden calls, input numbers, address book.
So, now you can dodge those annoying unwanted calls. Wishing you all the success.