My policy for calls from unknown numbers:
1 call: very likely spam; let it go to voicemail.
2 calls: Someone genuine is trying to reach me; let it go to voicemail. Listen to voicemail as soon as it arrives.
3 calls: emergency, pick up right away.
Exception: PagerDuty calls; pick up on first ring.
My wife is aware of this policy of mine. And I store kids’ school numbers in contacts.
I too will often not answer the phone if it's an unfamiliar number, but I do answer if it's the local area code which is not the area code of my wife's and my phone numbers since I figure it's more likely to be something legitimate like a call from a school or a local business where maybe I've forgotten I had placed an order or left dry cleaning and my stuff is now ready. If she had this policy, I would have spent less time waiting to get the combination.