I don't know over what time period, but I've had my main number for well over 15 years. I still don't get spam phone calls. I've had my business number for probably 6 years and it also doesn't get spam.

However, I've got a throw away number that I cycle out every few years for a few bucks and I get endless spam calls on it. Apparently I'm getting numbers that people have given up because they got too much spam. Now I'm worried if I ever need to change my main number I'll start getting crazy amounts of spam calls. Because for the throw away number I just check it once a week or if I need to get a code. I don't have the calls forwarded to my phone so I literally do not care about the spam.