What a dilemma! [groan]
TBH I think you need to manage your boss. Do you have caller display? If so, just don't answer - it saves having to address the issue directly, but will still get the point across once it happens a few times.
Or you could just say to him - stop phoning me at homebe blunt with him and tell him to stop.
Are you on call? What sector do you work in?