Hi @Daviddd, thank you for your question!
You can either block a number from the call log, or add it yourself. To block it using the call log, tap on the interaction/number > Block number > Block.
If you want to add a number on your own, open up the Phone application > tap the three dots in the top right corner > Settings > Block numbers > "Add number" and type in the number you want to block > Block. If you ever want to remove a number that you have previously blocked, you can do this in this menu as well by tapping the "x" next to the number.
I hope that answers your question! 
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