The actual answer unlike what stated by others is that phone calls are highly insecure and non private.
Telecommunications run over very outdated protocols that lack proper security and can rather easily be evesdropped. See also Veritasium: Exposing The Flaw In Our Phone System
You really should not rely on traditional phone calls for sensitive conversations and rather avoid having them anywhere possible.
I would not be to sure about calls not been retroactively recorded. Think a bit like of the body cams that can go back in time when an officer presses record. Let’s say it wouldn’t suprise if such systems exist.