Work on his phone identified a significant amount of use around the time of the collision.
In police interviews, Marston replied ‘no comment’ to all questions on how he had been able to unlock and use his phone.
Previous driving endorsements, including six penalty points for using a mobile phone while driving, were aggravating features in his sentencing, police said.
Investigating officer Charley Spriegel, from Surrey Police’s serious collision investigation unit, praised Mr Potkin’s family for remaining “incredibly dignified throughout the police investigation and court hearings”.
She said: “This should serve as a harrowing reminder to everyone who drives on our roads, that using a mobile phone behind the wheel can have horrific consequences.”