When I got my iPhone 8 in April, I used a cell phone number I'd had for years. The very next day I started getting 5 or 6 spam robocalls a day. I blame both Apple and AT&T. So I started getting busy with anti-robocall stuff. All the major cell phone companies provide basic defense for that. More active things are apparently in the works.
Download an app called Verizon Call Filter, available now for iPhones, and soon coming for Android. As of early April, Verizon stopped charging for basic service, which labels suspected robocalls and gives you three options based on risk level for how many to block. (Don’t let Verizon’s outdated description in Apple’s app store confuse you; there really is a free version now once you download the app, and there’s no need to sign up for a 10-day free trial.) If you pay $3 per month, you’ll also get caller ID.
The source of this info came from an article I saw in the Washington Post, last April. See the attached PDF.