Phoenix, who plays Cash in new biopic Walk the Line, was thrilled when the country couple invited him to dine with them and discuss the movie.
The actor lights up when he recalls the magical evening at the Cash's place: "I met him (Johnny) about six months before he died. We had dinner and we went into his living room and he picked up the guitar and started strumming.
"He leaned over at one point and apologetically said, 'I'm waiting for June to get my nerve up.' I thought, 'Johnny Cash is waiting for someone, he's nervous.'
"June came in and he said, 'Will you sing a song with me?' and she said, 'Oh yeah, Johnny.'
"It's such an extraordinary story. Their love endured through so much."
Cash died in September 2003, four months after his spouse June passed away (MAY03).