The sentence was the lowest term Senser faced for her two criminal vehicular homicide convictions, the (Minneapolis) Star Tribune reported.
She could have received a maximum sentence of 57 months.
Senser, 45, publicly apologized to the Phanthavong's family before she was sentenced.
"This isn't about me. I hope you can believe me that I never saw your son that night. And if I had I would have stopped to help him. I take full responsibility for his death," she said. "I wish I could go back to that night and change things. I don't know why, I don't know why ... our fates have come together but if you let me I will do whatever I can to honor his name."
Police said Senser's sport-utility vehicle struck Phanthavong, 28, a chef from Roseville, Minn., as he was putting gas in his stalled car on a highway exit ramp on the night of Aug. 23, 2011, in Minneapolis. He died at the scene.
Senser, who left the scene, said in court she thought she had hit a construction cone or barrel on the ramp that night, not a person.
The day after the accident, Senser turned her SUV over to authorities through an attorney but didn't come forward as the driver until nine days later, the Star Tribune said.
Joe Senser was a tight end for the Vikings in the early 1980s.