Driving a vehicle required careful observation and concentration, and distraction could have serious consequences.
Mr Campion said the danger was two-fold.
"One, you have to take your eyes away from the road and, two, you're concentrating on something completely different to what you should be. Really, it's a no-brainer to be perfectly honest."
Only a small minority continued to flout the law and he was encouraged to regularly see people pull to the side of the road to use their phones.
Bay of Plenty district road policing manager Inspector Kevin Taylor said there had been an increase in infringement notices each year.
There had been a number of serious injury and fatal crashes in the Bay of Plenty in recent years relating to cellphone use, he said.
One of those involved Rotorua truck driver Garry John Galvan, who was found to be texting at the time of a fatal crash in 2011. Using hands-free kits was legal but Mr Taylor encouraged people not to use phones at all while driving.
"It's not actually what you are doing with your hands that's the problem, it's what you are doing with your brain."
Tauranga driving instructor Carl Winter said he was concerned about the number of people he saw using phones while driving.
"You're brain's distracted. You're not concentrating on driving," he said.
"You've got to be fully focused. Even people talking to you can distract you."
Mr Winter said the best solution was for people to turn off their phones while driving, so they were not tempted or distracted by it ringing.
The number of people he saw using their phones while driving suggested the ban was not working, he said.
Drivers using handheld mobiles can be fined $80 and given 20 demerit points.