The decision to close it and merge with nearby Woolston School to create a 465-child super-school next January came as part of the Government's $1 billion shake-up of post-quake Christchurch schools.
The ministry said the school suffered quake damage, and it made sense to merge its small roll of 163 with another small roll.
The decision caused mass upset with the decile 1 school's pupils, teachers, and the community.
The school has employed counsel Mai Chen, who last year successfully argued for a High Court judge to overturn the Government's decision to close Salisbury School, which was deemed unlawful.
The Phillipstown school community were particularly angry at a perceived lack of consultation, and Justice Fogarty agreed.
While the judge was certain the Education Ministry conducted consultation "in good faith'', it had failed to meet the requirements of the Education Act.
He found that the importance of the cost of Phillipstown continuing on its site was "mistakenly played down'' and that ``for a miscellany of reasons, the financial information being relied upon by the Minister was not reasonably broken down and explained in a manner which would have enabled a critique''.
"These two failures of process led the Board to not make submissions on the costs, other than to complain about the inadequacy of information,'' said Justice Fogarty.
"These failures of process mean that the Minister has not lawfully merged Phillipstown with Woolston.
"Her decision is declared unlawful and is not valid.''
There was no error of law in the `Rationale for Change' package delivered to the Phillipstown Board, which clearly expressed the combination of a low roll and high remediation cost.
It is now open to Ms Parata to "continue'' the consultation
"I deliberately use the word `continue','' said Justice Fogarty.
``The breach of natural justice can be corrected without requiring the consultation to start again.''
Ms Parata could then make another decision, he said.
Ms Parata has responded by saying she will review carefully the outcome of the judicial review brought by Phillipstown School.
"We will urgently examine Justice Fogarty's decision, and our options, including continuing consultation on the issue that was of concern to the court,'' she said.
"These are unique circumstances and, while it is never an easy decision to merge a school, it is clear that Christchurch education needs to be organised differently post the earthquakes.
"I will not be making any further comment until I've had time to consider the decision and receive Crown Law advice.''