No. iPhones do not have a master list of "all unknown numbers." You cannot accidentally "block all strangers" and then unblock them. The only way an unknown number is blocked is if you manually did it, or if you turned on "Silence Unknown Callers" (Method 2).
Many iPhone users think they have blocked unknown numbers, but they actually have a feature called turned on. This feature sends calls from numbers not in your contacts straight to voicemail without ringing your phone. If you want to "unblock" these unknown numbers, you need to turn this feature off. how to unblock unknown numbers iphone
Fixing the issue where your phone doesn't ring for people not in your contacts. Many iPhone users think they have blocked unknown
Scroll down to (or Silence Unknown Callers in some versions). Fixing the issue where your phone doesn't ring
Scroll down and tap , then select Phone (or just search for "Phone" in Settings). Tap Silence Unknown Callers (under the "Calls" section). Toggle the switch to Off .