Derek Grant, 38, had pleaded guilty to the culpable homicide of Patrick Bradley, a serial offender described in court as "a man of violence".
Grant was blinded in one eye during the fight when Bradley stabbed him through the left eyeball and now has a lifelong disability.
It emerged that the victim, who had a lengthy criminal record, had already been jailed for stabbing someone through the eye.
After sentence was passed at the High Court in Livingston yesterday, a member of Grant's family branded the outcome "a farce".
The woman, understood to be Grant's wife, added: "That guy was an animal."
And, as the family left the court building, the woman revealed she and her family now feared reprisals in their home town of Greenock, Renfrewshire.
Grant, and his three sons were originally charged with murder after Bradley robbed his 19-year-old son Jordan - a politics student - at knifepoint.
The Grants used the Find My iPhone app on August 30 last year to locate the stolen mobile. Grant then left his home in the town's Wellington Street with Jordan and his two younger sons Lee, 17, and Jamie, 16.
The father had taken a knife to confront Bradley, a decision described by defence counsel Iain Duguid as "a huge mistake".
When they spotted the robber, who was not known to them, Derek Grant ordered him to hand back the stolen phone. Bradley, 29, reacted by plunging a knife through Grant's left eye, blinding him.
Severely injured, Grant stabbed Bradley five times with the blade he had brought with him.
Three of the blows landed in Bradley's chest, causing fatal injuries. He died in hospital later that day.
Passing sentence, Judge Lord Boyd said a victim statement from Bradley's parents made clear he was "a loving and caring son whose death at your hands has left them, as his mother says, 'broken-hearted'." He added: "Nothing I can say or do can alleviate that pain."
However, Lord Boyd highlighted there was another side to Bradley's character
He told Grant: "He was a man of violence. He had 10 convictions for assault, five of which were on indictment and included assault to severe injury and assault to severe injury and permanent disfigurement.
"But you did not know that. What you did know was that earlier that night Patrick Bradley had robbed your son of his mobile phone at knifepoint.
"Had he been caught it seems likely given his record he would have been prosecuted in this court, the High Court, and on conviction would have received a High Court sentence. As it happens, you had the means to bring him to justice because the phone had been easily located by the Find My iPhone app.
"All you needed to do was to phone the police and give them the information.
"However, you armed yourself with a knife and, along with your three sons, went looking for him."
Lord Boyd acknowledged Grant had lost an eye as a result of being stabbed and the disability had effectively ended his career as a delivery driver.
He described Grant's conviction as a "tragedy" for his family and told him the proud educational record of his sons was a credit to him.
He went on: "I take into account you will have to live with the physical consequences of that event for the rest of your life and have reduced the sentence accordingly.
"Nevertheless, the fact is you took the law into your own hands."