Many people use disposable emails to preserve privacy and enhance digital security, so why not do the same with your phone number?

Certainly in the US, where spam calls are a major issue, this does feel like a logical route to take. Terence has a good write-up of the strategies that they use to achieve this, as well as providing an overview of some past attempts at services that could help out.

On the current best option for disposable phone numbers:

The easiest way is to get a dual SIM phone. I have my main SIM which holds my primary phone number. That's the number used by my family, my banks, and anyone vaguely trustworthy. My second SIM contains a free disposable PAYG SIM.

And once I start getting too much spam to that number I throw the SIM away and get a new one with a new number.

On an alternative option, SIP calling plans:

Or, you can set up a SIP calling plan. Install an app and have calls automatically routed to you.