Fifty-plus inmates watched the movie Tuesday as the actor and others, including musician Shooter Jennings, who plays father Waylon Jennings in the movie, and toured the facility with prison officials.
Cash's Jan. 13, 1968, performance in the prison yard cemented his hardscrabble image and became a popular live album.
Dressed head to toe in Cash's trademark black, Phoenix performed several acoustic songs with Jennings at the prison's Greystone Chapel, including Cash's "Folsom Prison Blues." Jennings played his father's song, "I'm a Long Way From Home."
Phoenix apologized for his "rusty" performance, saying he had not played since the movie's completion.
"I don't know if you've noticed but I've messed up like 40 times," Phoenix said. "I'm all over the place."
One inmate asked Phoenix if he learned to play guitar for the movie.
"John wasn't (Jimi) Hendrix," Phoenix replied. "It was real simple ... we rehearsed a lot."
Noting that co-star Reese Witherspoon, who played June Carter Cash, couldn't make it, Phoenix said: "I know you guys would probably rather see Reese."
Phoenix has been considered a likely Academy Award nominee for his performance as Cash, who died in 2003 soon after his wife's death.
An Oscar win by Phoenix would make it the second-straight year the best-actor honor went to a performer playing a beloved, recently deceased American singer. The 2004 Oscar went to Jamie Foxx for his portrayal of Ray Charles in "Ray."
Warden Matthew Kramer presented Phoenix with a prison-made license plate bearing the actor's name, and gave another to Jennings bearing the movie's title.
The event was organized by Prison Fellowship, a group that runs Bible studies and other educational programs in prisons.
Fellowship spokesman Joe Avila said the movie's message would be good for inmates because Cash's "whole life was a message of redemption."
"The movie is about how he screwed it up really bad, and he turned to Jesus Christ to help him change," Avila said.