This article explains how to unblock a phone number on an Android smartphone. Instructions apply to Android 6 and later.
How to Unblock a Phone Number After Blocking It on Android
The Phone app has a list of all the numbers you’ve blocked. This makes it easy to unblock a number so you can receive calls and texts again. Here’s how to find this list and unblock the number:
Tap the More icon. This icon looks like three vertical dots.
Tap Settings > Blocked Numbers.