Looks like MS finally listened. An update is forthcoming which will add the option to remove a device from Phone Link:
https://www.xda-developers.com/microsoft-fixes-annoying-phone-link/
Call me paranoid, but I think it's timely to reflect that Microsoft might approach this in such a way that even though we can already remove our old devices from the Phone Link registry, Microsoft would still retain that registry for its own interests. In other words, it is possible that they could create the illusion that we have control over our data, while Microsoft retains it regardless of whether we see it appear in the registry. And of course, this also extends to other areas of the entire Microsoft ecosystem where our data interacts with them.