I will not answer calls from numbers I don't know.
It is best to not even answer any call from an unrecognized number. If it is important, someone will leave a message or call back.
The simple fact that you answered the call lets the sender know that it is a valid number and they sell it. They do not even have to be selling a valid product. If you press any key, then they know it is a valid number and if you say anything, especially if it is offensive, then you guarantee that your number will be sold.
About 5 months ago, I stopped answering calls from unknown numbers and I have seen a distinct decrease in all calls even valid commercial ones. I used to receive about 2 - 3 calls a day and now it is down to about 1 a week.
Records are being kept that increase the validity of your number being active based on the number of times you have answered these phishing calls. Those numbers with the highest connect rate net the most profit for the phishers and are highly prized for the commercial industry.