Your phone will block calls from private or unidentified numbers. You'll still receive calls from phone 
numbers that are stored in your contacts.
 
Tip: You can also automatically identify potential spam callers and easily block them with Google Caller 
ID & spam. Learn how to set it up.
Unblock a number
From the   Phone app:
1.
Tap   > Settings > Blocked numbers.
2.
Tap   by the number to unblock.
From the   Messages app:
1.
Tap your profile icon   > Spam & blocked.
2. Tap the blocked conversation.
3. Tap Unblock.
Contacts, calls, voicemail : Phone calls 141