Dont go giving out your phone number to people/companies all the time. Even more 'trustworthy' companies often onsell your data, and can lead to an increase in spam calls. I only give out my phone number if I know that the company will need to contact me directly or I often just leave it blank.
If you are getting alot of spam calls there are a number of steps you can take - first there are apps that block calls from certain numbers. If these don't work you could look at changing your number completely. I know some companies 'recycle' their old numbers though so this could be gamble.
I think I am a bit trustworthy because I usually pick up even when I don't recognize a number. If you aren't happy with this you can Google the number followed by a word like scam/spam and there are websites where people say whether the number is a suspected scam.
If all this fails, then the best thing you can do is to disconnect and live off the grid - this will stop the spammers calling you for good :P
There are call apps that helps you identify spam calls like true caller for example, it tells you it is a spam call and the number of people that have it blocked. All you have to do is add it to your list and such call won't come again.
Don't answer numbers you don't recognize.
If you do answer numbers you recognize, and you frequently get spammed, you need to be firm with these people, and tell them you are not interested, and that they are wasting their time.
If they don't heed your wishes, which they likely will not, you should just hang up every time they call, and hope they get the hint.
If all else fails, and you are getting spammed so much you can't take it, you might want to consider changing your phone number.
I have a feature on my phone which we all have which is call identity.
If you don't recognize the number and it says spam then block it. I used to get 2 or 3 calls a day from people trying to sell me things and now I don't.