Not sure why people see their phone number as something private?
FWIW, I've heard some people saying they avoid it because of spam, I've been on my local anti-spam list since I got my current phone number, and receive about 1 spam call every week or something. Maybe there is one for where you live too.
I command a significant budget and even with a lot of effort to not proliferate my phone number, I get at least half a dozen spam or sales calls a day. I can't imagine how bad it would be if I didn't attempt to protect it. Perhaps it would be the same and I should just give up, but I'm not willing to try.
The other side of the coin is that it's just none of their business. They don't need my phone number to sell me SaaS software. There is no upside for me to give it to them.
I don't think so, I've had friends and acquaintances that had the same issue as you, multiple spam calls per day. I helped them add themselves to their national list, and after a month or two the constant spamming stops.
I think you might just be unlucky living in country that doesn't have such list that works OK. I've lived in multiple different countries so far in my life, and it's been the same thing in all of them, adding myself to the list eventually makes the spam stop.