The 36-year-old revealed Beckham's secret during a radio show on talkSPORT when speaking about a previous conversation he had with the retired midfielder during international duty with England.
"Many, many years ago in a treatment room with England, we were talking about this," the Daily Star quotes Murphy as saying. "And David Beckham, I remember it well, guess who he said? Cherie Blair!"
Blair is 20 years older than the former Manchester United star.