I have set my land line and cell phone to accept only calls from my contact list. I haven't received a spam call in six months.
For this to work you must have a good contact list. I had one on my PC that had about 600 contacts developed over 20 years. I transferred it to my cell phone and from there to OOMA which I use for my landline. Then I set both to accept calls only from contacts and send the unwanted calls to voicemail. That way if I get a call I want that is not on my contact list I can add the number.
Here are the directions from Verizon to do this:
Follow these instructions to limit all incoming calls to people on your Contacts list:
Navigate to Settings -> Do Not Disturb.
Toggle Manual ON (green slider) to enable Do Not Disturb (DND), or schedule a time for DND to automatically switch on.
Tap Allow Calls From.
Select All Contacts.