More than nine million people still illegally make or receive calls while driving, new research from the RAC suggests.
This is despite the doubling of penalties for the offence in March 2017, to six points and a £200 fine.
The motoring group has labelled the problem an “epidemic”.
The research also found that 40% of drivers check texts, email and social media while sitting in traffic – despite the fact it’s against the law.
More than 1,700 drivers were questioned in the survey – with 23% admitting to illegally making to receiving calls.
With 40m drivers in the UK, it would mean 9.2m people breaking the law in that way, if the results were extrapolated.
Only one in ten said they did not know about harsher penalties for being caught.
RAC road safety spokesman Pete Williams said: “It is clear we have a hardcore of persistent offenders who believe they can get away with it.”
The number of people who illegally make or receive calls is falling – from 31% in 2016 to 23% this year.
Of those who were aware of the tougher penalties, 58% said they had never used their phone illegally behind the wheel.
Another 16% said they’d stopped completely since the law change.
Of the 15% of drivers who the RAC calls “hardcore” law breakers, 57% were men.
By Richard Westcott, Transport Correspondent
These numbers have fallen compared with last year, but the impact of doubling the punishment clearly hasn’t deterred millions of drivers from breaking the law.
One in ten told the RAC that they did it because “I can get away with it”, which is why the group says a big drop in traffic police numbers is partly to blame.
It’s interesting how many people still check their phone whilst sitting still in traffic. The fact that nothing’s moving clearly makes it feel safer – but beware, it is still illegal.
Last year, this survey had the state of the roads as drivers’ number one worry. Now it’s people using their mobile phones.
It’s still OK if you have a proper hands-free unit.
The RAC report also raised concerns about the fall in the number of road policing officers, which it described as a “massive” 30% between 2007 and 2016.
Mr Williams says the RAC fears the problem of mobile use may get worse as a result of this fall.