In the scam in question, you (as the victim) - hang up the line. You then pickup the receiver to call your bank, via the number on your card.

The scammer, when they hear you hangup, plays a dial-tone down the line, so when you pickup the receiver, you have the impression that the line is clean.

You start to dial, they stop the 'dial tone', play a fake calling tone, and then 'answer' the call.

This would be incredibly malicious and difficult to detect even for the most skeptical of users.