It’s probably more accurately described as extortion phishing. With blackmail, I think you actually have to have damaging information that your withholding in return for payment (or other benefit). But this is clearly a non-tatgered phishing attack sent to many individuals in the hopes of extorting a payment, without the sender actually having anything damaging on the recipients.
Maybe this phishing definition and background on why that term was coined will resonate better.
From https://www.csoonline.com/article/514515/what-is-phishing-examples-types-and-techniques.html
Common phishing schemes involve getting someone to divulge some form of personal information but not all fall into this category. Phishing attempts can involve trying to trick the target into taking some form of action, including making a payment.