The request was denied and an argument broke out.
Mr Alatipi told the man to return to his cell, at which point the prisoner claimed he was assaulted.
Mr Alatipi said the prisoner had taken the decision to refuse him a phone call badly and at one point racially abused him, prompting Mr Alatipi to lock him in his cell.
Staff from the Corrections Department investigated the incident and found Mr Alatipi guilty, despite police choosing not to lay charges, the decision said.
Mr Alatipi had asked the department to delay its investigation until after the police inquiry - as they had done in other cases - which they declined to do.
"Corrections provided no reason or explanation for not agreeing to follow that same procedure in Mr Alatipi's case," Jude Ford said.
The department also failed to interview other prisoners about the incident, which Mr Ford said, could have helped corroborate or cast serious doubts over the assault allegation, Judge Ford said.
"A disturbing aspect of the investigation...was the way in which the investigator appeared to passively accept from the outset everything that Prisoner X told her about the alleged assault."
He found the department did not have a sufficient and reliable evidential basis for concluding that Mr Alatipi had assaulted the inmate.
Judge Ford ordered Mr Alatipi be reinstated to his job, be awarded $20,000 compensation for humiliation, loss of dignity and injury to feelings, and receive three months' remuneration in lost wages.
Corrections' Lower North Region regional commissioner Paul Tomlinson said the department acknowledged the decision.
"We are presently reviewing this judgment and deciding on what options are available to us to respond."
The department would make a decision about its response over the next week, he said.
Mr Alatipi could not be reached for contact.
