There’s a good chance it’s made up, because some of the details are wrong.
For one thing, Kavanaugh and ACB are the two most junior justices. Gorsuch was appointed in 2017, Kavanaugh in 2018, and ACB in 2020.
If the caller actually worked at the Supreme Court, I do not think he or she would get these details wrong.
I’m a little suspicious about it too. But, I don’t think the caller was referring to Gorsuch as one of the two most junior justices. Here’s the line in question:
“You are forgetting what your role here is Neil, and I don’t want to hear from the two junior justices anymore. I will tell you how you will vote.”
So it sounds to me like he’s talking to both Neil AND the two junior justices (Kavanaugh and Barrett), not claiming that Neil is one of the two junior justices.