So the cop just says, "Hang up the phone now, sir."
It's within their rights to have you refrain from calling anyone or talking to anyone while they are conducting an investigation. Your lawyer could be in the car with you and they'd still have the right to tell the two of you not to speak to each other.
Now, a law requiring the cops to stream video to a civilian review board during a stop might yield results. But, no, you don't get to call your lawyer during a stop.
Sorry.