Tap on the number or contact, then tap the info (i) button.
He opened his Phone app (the green one) and tapped the in the top right corner. A menu dropped down, and he selected Settings . There it was, like a little jail for unwanted callers: Blocked numbers .
Tap the red minus (-) icon next to the number you want to unblock. How to Unblock Unknown/Private Numbers
If you use apps like Truecaller, check their settings, as they might be overriding the phone’s native settings.