A driver who was looking at his phone before he hit two police officers in western Sydney last year has been sentenced to a maximum of three years and eight months in jail.

Key points: The judge said Thornton had good prospects for rehabilitation

The judge said Thornton had good prospects for rehabilitation Thornton wrote two letters expressing "deep remorse" for his actions

Thornton wrote two letters expressing "deep remorse" for his actions The police officers are both back to work on limited duties

Jakob Thornton, 23, pleaded guilty to two charges of dangerous driving occasioning grievous bodily harm last year.

Senior constables Jonathan Wright and Matthew Foley were setting up an RBT site on Campbelltown Road at Leumeah when Thornton ploughed into them.

Senior Constable Wright's foot and part of his lower leg were amputated due to his injuries, while Senior Constable Foley had to have a titanium rod inserted between his right knee and ankle.

Thornton told police that night that he was receiving and sending messages on his phone before the accident.

He will be eligible for parole in January 2021 and has been disqualified from driving for three years.

The crash happened in February last year, just after 9pm.

NSW District Court Judge John Hatzistergos said in his judgement that Thornton had immediately exited his vehicle with a first-aid kit, but was stopped by other police officers from approaching those he had hit.

Thornton told officers at the scene he had been on his phone, and in a late-night police interview said he had been looking at his phone for about 20 seconds and had driven around a bend in the road without looking.

Judge Hatzistergos said Thornton's "actions were clearly not impulsive, but sustained".

"It was an irresponsible abdication of responsibility for an extended period from someone who selfishly prioritised communications with his girlfriend, disregarding the need for vigilance when driving a motor vehicle," he said.

'A stupid mistake'

The judge said Thornton had good prospects of rehabilitation and a low likelihood of reoffending.

He referred to two letters Thornton wrote expressing "deep remorse for his actions".

Jonathan Wright (left) and Matthew Foley were conducting random breath tests when they were struck. ( GoFundMe )

"My main regret is obviously concerning the injuries to the two officers, one of whom lost his lower leg," the judge quoted from the letter.

"For the moment, all I can do is apologise and pray that they both recover as well as could be expected.

"Causing that much damage for such a stupid mistake has weighed very heavily on myself and I am sure that it will follow me for the rest of my life.

"What I did was not worth the risk of affecting the lives of all involved and I truly hope that through my grave mistake, people can learn, so that all of the pain I caused was not for nothing."

Judge Hatzistergos said Senior Constable Foley suffered pain to his right leg and constant swelling, is unable to kneel or run and has visible scarring.

Senior Constable Foley has returned to work a few days a week but can no longer drive a police car or interact with the public. He also suffers bouts of depression and PTSD.

Senior Constable Wright suffered chronic phantom limb pain and has now been fitted with a prosthetic leg. He is now back at work three days a week.

He is unable to do physical activities like mountain biking with his family and home renovations, which he regularly did before the accident, and now falls often due to the pain in his leg.