I told my boss at the wine store when I got fired over the phone that I wish she had the courage to do it in person and that I thought she wasn't much of a person for not being able to look me in the eye and fire me considering the work I had done for her. When I got off the phone I thought she was going to cry. But you know what? People should say that, they should expect enough human courtesy from their employers. I am not a machine.
I wonder what would have happened if you or SE had responded to the "you're fired" With something like "What?" pause then say "That's you, isn't it, Bill?" (some imaginary friend's name) "You really had me going there for a moment. You even sound a lot like our manager, although he doesn't sound as whiny as you. Ha! Ha! But I wish you wouldn't make prank calls while I'm at work. I've got a lot to . . . [ mention here all the great things you're doing for the company and how you're keeping moral up despite the idiot management]. So call me back AFTER work. Bye." And hang up.
If they call back just say "Sorry, Bill, I told you I can't talk right now. And the jokes getting old. I've got work to do. I'm the only one keeping this store afloat." Hang up again.
Then they'd have to come in and fire you in person.
I once worked at a place where the company accountant told me that he didn't trust the CEO. How's that for a bad sign? They had a huge turnover of professional people. You'd have thought it was a fast food place. And each time the entire software team turned over they'd pretty much be starting the whole project over from scratch. Stupid way to run a business.