This number has called a few times, claiming they are the "IRIS" and that I am being sued. Just called to say this was the final attempt. Very poor quality robot voice, was cutting in and out. Caller ID says Cheyenne, WY. I'm fairly certain the IRIS would mail a letter, never call.
I called the number and they said I'd underpaid my taxes by $7,000 for 2010-2015 due to a calculation error. They couldn't tell me what the calculation error was. When I said I didn't believe they were a real IRS agent we suddenly got disconnected. FRAUD!