Probably a scammer using a spoofed phone number. They disconnected as I answered the phone and when I called the number back, a recording told me that the phone number was not in service.
Caller ID is just the number. They leave no message.
I call back after hours (using *67 to block my number). I hear, "<tone> We're sorry the number you are trying to reach is no longer in service. <tone> We're sorry your call can not be completed at this time. Please, hang up and try your call again later. Thank You."
So they don't identify themselves on caller ID, don't leave a message, and can't be called back. Smells like a SCAM.