Open the Phone application and select the menu button (three dots) in the upper right corner to see your Android's prohibited list. Tap "Settings" and then "Block numbers." Here is where you'll find a list of restricted phone numbers. You can tap a number to unblock it or the "Add number" button to add a new number to the block list. If you want to block an unknown number, you can tap the "Block unknown anonymous callers" switch at the top of the screen. This will block all unknown numbers from calling or texting you.