Alleged terrorist Omarjan Azari has been denied bail, with a Supreme Court judge finding his being held in the onerous conditions of Supermax does not constitute "exceptional circumstances".

On Thursday Justice Peter Garling said the prosecution case against Mr Azari, 23, of Guildford, is "reasonably strong".

Mr Azari is accused of helping to plan a terrorist act in a phone call with Mohammad Ali Baryalei, allegedly Australia's most senior member of the terrorist group Islamic State, who was believed killed while fighting in northern Syria in October last year.

"What you guys need to do is just pick any random unbeliever," Mr Baryalei allegedly said during the phone call in September last year. "When finished put the flag of the state in the background and film it and send it off."

During a bail hearing last week, Justice Garling​ ordered the Crown to provide any material or evidence to show why Mr Azari had been given the state's highest security classification - AA - and a cell at Goulburn Correctional Centre's High Risk Management Unit where he is awaiting trial, which could yet be a year away.

On Thursday Peter Neil, SC, for the Commonwealth DPP, provided affidavits from Corrective Services and the Australian Federal Police.

Justice Garling said after reading Corrective Services' reasons for classifying Mr Azari as "extreme high risk" he concluded "there is nothing obviously wrong about that classification".

Such inmates are assessed to be an "extreme danger" to other people, the running of the jail and the peace and security of the community. They are also considered likely to incite other inmates to participate in or commit terrorist acts, the court heard.

Mr Azari has been in custody for almost 12 months since he was arrested at his home during the largest counter-terrorism operation in Australia's history in September last year.

The raids came three days after the intercepted phone call between Mr Azari and Baryalei.

Mr Azari is charged with conspiracy to murder and knowingly making funds available to commit a terrorist act.

A charge of conspiracy to commit a terrorist act has been withdrawn and replaced by a charge of "doing acts in preparation to commit a terrorist act", which carries a maximum term of life imprisonment.

In applying for bail, Mr Azari's barrister Winston Terracini, SC, said his conditions in custody are "harsh and oppressive" and "unacceptable and unnecessary".

He is not allowed to speak Arabic, although the court heard an evaluation is under way into whether an exception to the Supermax ban on Arabic will be granted to Mr Azari. Legal visits are restricted and done via video-link as no face to face contact is allowed.

But Justice Garling said the circumstances around legal visits were not relevant to the question of bail.

Much of the evidence against Mr Azari comprises intercepted telephone calls in which English, Arabic and an Afghan dialect are spoken.

The original translation of a phone call between Mr Azari and Baryalei said the two talked about "abandoning" the terrorism plan so as to avoid detection by the authorities.

Mr Terracini said a second, official translation now reads "postpone" rather than "abandon".

In denying bail, Justice Garling said notwithstanding the translation issue, "I have concluded that the conversations relied upon could support the charges".

Mr Azari is due to appear in the local court on September 23.