Prosecutors say a New Zealand man accused of trying to enter Syria to fight alongside extremists used four different phones to have coded conversations about "a big job" days before attempting to fly to Turkey.

The allegations in Victoria state Supreme Court on Monday come two years after Amin Mohamed was stopped in the Australian city of Brisbane when trying to board a flight to Turkey.

Mohamed was later charged with three counts of preparing to enter a foreign state to engage in hostile activities. If convicted, he faces up to 10 years in prison on each count. He has pleaded not guilty.

Prosecutor Lesley Taylor told the jury they would hear recorded phone conversations in which Mohamed used coded language about his upcoming trip to avoid detection by authorities.