Research by the Royal Automobile Club (RAC) said 47% of motorists aged between 25 and 34 admitted making or receiving calls while driving, up seven percent from the previous year.
A quarter (25%) of drivers in all age groups - equivalent to 10m people - said they had done so, an increase of one point from 24% in 2017.
The RAC found 36% of motorists in the 25-34 age group and 29% of those between 35 and 44 used a phone to send texts, post on social media or check emails while driving, a 10% rise on the previous year and back to the same level as in 2016.
Thirty-nine percent of drivers in the 35-44 age group admitted to making or receiving calls while driving, and 54% said they do so while stationary.
Almost a third of drivers (30%) aged 25 to 34 admit to taking photos, selfies or videos while driving, more than double the proportion of all drivers who do this (16%).
The worst area is London, where 52% of drivers say they make or take calls using a handheld phone while driving, up 16% from 2017 and higher than in 2016 (47%).