Spam is any unsolicited call. These include calls that you have not given permission to call you (at least not formally), but may be from legitimate organizations or individuals e.g. non-profit organizations or political robocalls.
Scam is phone number linked to a some form of scam or fraudulent activity. There are several types of scams. To learn more about this, please refer to https://www.consumer.ftc.gov/articles/0076-phone-scams.
So, all scam calls are spam, but not all spam calls are scams.