Cleghorn was found guilty of 16 sexual assault charges against three victims, in total, which included 13 charges of sexual violation by unlawful sexual connection, two charges of indecency between males and one charge of contracting for commercial sexual services with a person under 18.
The court heard that in 2018, Cleghorn offered some work to a 16-year-old boy.
He said the job "might seem a little dodgy" but would take less than 20 minutes.
Cleghorn picked the boy up from school and took him to another man’s house.
The boy was asked to perform a sex act on the man in exchange for $50.
He refused, and Cleghorn warned him not to tell anyone or he would get in trouble.
The court heard Cleghorn had been sexually offending since he was 14 and his first victim was 4 years old.
Between 1985 and 1993, the defendant sexually violated the boy on multiple occasions and coerced him into reciprocating the sex acts by bribing him with money and jewellery.
On Cleghorn’s 23rd birthday he gave the then-12-year-old victim alcohol and performed a sex act on him and asked him to reciprocate.
The abuse against the first victim continued even while Cleghorn was in a relationship and only stopped when Cleghorn was about 25.
Another victim was a 4-year-old girl who Cleghorn sexually violated once between June 1990 and December 1991.
He exposed himself to her and made her perform a sex act on him.
Yesterday, the court heard that the girl did not completely understand what had happened at the time, but later understood the offending.
In a statement to the court she said it felt like "a secret shame" that she had to hide because she felt bad about what happened.
She hoped the defendant would seek help and stop hurting people.
Yesterday, the victim who Cleghorn attempted to prostitute told the court he was "shocked" when he was taken to another man’s house.
"He took advantage of me for his own sick pleasure," the victim told the court.
"I was really grossed out by what Phillip asked me to do."
Judge Michael Turner noted Cleghorn had a criminal history which included violence, dishonesty and firearms offences.
He said although the defendant was young when he first started sexually offending, it continued into adulthood.
The defendant continued to claim he was innocent, making his prospects of rehabilitation poor, Judge Turner said.
Cleghorn had "engineered" situations which allowed him to offend against vulnerable children.
Judge Turner sentenced Cleghorn to 13 years’ imprisonment.
He was automatically added to the Child Sex Offender Register.
