Staff were monitoring the prisoner's calls as a matter of routine when they recognised Tracey Storey’s voice on February 5, said prosecutor Michael Jones.
She was suspended from duty as a substance misuse worker in the prison’s healthcare department and, while being escorted from the prison, said: "I have been dreading this day. I have been waiting for this moment."
The court heard there was no sexual contact between the pair, and the relationship lasted from November 11, 2019, to February 6, 2020.
Storey's manager became concerned after their meetings took longer than usual and Storey “unusally” met the prisoner in reception, after his transfer from HMP Doncaster.
The inmate called her personal phone nine times between October and December 2019, and listed her personal number under the name of his ex-partner.
He was later transferred from HMP Moorland to HMP Leeds.
Richard Barradell, mitigating, said he accepted prison security had been compromised, but Storey’s wrongdoing went no further than “sexual chat.”
He said she had no previous convictions, but was "vulnerable" and "at a low ebb" because of bereavements at the time of the offending.
"She was struggling to extricate herself from this relationship,” Mr Barradell said. “She is utterly ashamed and very, very embarrassed.
"She lost her job as a result and now works in a pharmacy. She was literally putty in this man's hands."
Storey, aged 54, of Coventry Grove, Doncaster, pleaded guilty to wilful misconduct in a public office at the lower court.
Judge Michael Slater told her: "In my view this does cross the custody threshold. You abused a position of trust. You were sufficiently experienced to be aware of the dangers of this type of liaison.
"What you did potentially undermines the moral authority of the prison service. Had it gone further, the outcome of this hearing today would be very different."
On Friday, the judge sentenced her to three months in prison, suspended for one year.