A driver trying to do the right thing after pulling over to use his phone has had his car allegedly stolen as he stepped out of the vehicle to talk.

NT Police said around 7:00pm on Monday night the driver of a Hyundai pulled over on Dick Ward Drive, in Coconut Grove, in Darwin's seaside northern suburbs.

Northern Watch Commander Senior Sergeant Garry Smith said the man had done "just about everything right" when he wanted to make the call.

"He pulled over into a safe area but things turned a bit pear shaped. He got out of the car, left it running and walked away from the car to make his call," Senior Sergeant Smith said.

"A 31-year-old male, not known to the driver, took advantage of the running vehicle, hopped in and drove off.

"The owner, in possession of his phone, terminated his call and called police."

He said the "new driver" of the Hyundai was arrested soon after and allegedly returned an alcohol reading of 0.291 per cent.

Senior Sergeant Smith, known in the Northern Territory for his expansive views on the behaviour of Territorians, was not impressed.

"I'm outraged! Another one who can explain his actions to the courts," he said.

Senior Sergeant Smith reminded drivers of the penalties of using an electronic device while driving in the NT.

"You must not use a hand-held mobile phone while driving, even if you are stopped at traffic lights. You can use a hand-held mobile phone while your vehicle is parked in a designated parking place," he said.

"Drive while using hand-held mobile phone equals $250.00 fine and a $40.00 victim levy."