They called me repeatedly 4 times over 20 minutes this afternoon. My iPhone answered the call to ask for more details and the computer at the other end of the line only said "We have detected an attempt to change the primary phone number assigned to your account. If this was not you, please press 1. If this was you, you may hang up."

There is no identification of which company they're calling from. They're making it feel urgent by calling every 5 minutes. It is a computer at the other end of the line. Phishing attack.

Did not answer the phone as I didn't recognise the number, although it flashed up as being from Woodburn (which I understand is a small town in NSW - I don't know anyone from that part of the world). The phone rang for a short time, then stopped abruptly before it could go to voicemail (ie no message was left).