The case dates to September 2016 when the accused, now 26, was driving in La Chaux-de-Fonds in the canton of Neuchâtel, reported news agencies.
The man composed two text messages and browsed the internet on his smartphone while behind the wheel, found the court, saying the technical evidence for this was “overwhelming”.
Distracted by his phone, the driver did not see a scooter and cut him off on a turn.
The scooter driver, in his 50s, attempted an emergency brake but fell from his bike and was hit by the wheel of the car.
The incident was captured by a surveillance camera.
“There was no other cause than the use of the phone,” said the court president, judging the defendant's use of the phone to be non-negligible.
He had been browsing an online shop at the time and had just completed a transaction when the car and scooter collided, claimed the prosecution.
The man denied browsing the internet during the journey and said he sent the two text messages before he set off.
“The truth is I didn't see the scooter. I'm really sorry. I don't know why I didn't see it,” he told the court.
His defence team said his only infraction was not observing the rules of priority on the road.
But the court convicted him of negligent homicide, rejecting a call by the prosecution for the more serious charge of murder by indirect intent, which would have incurred a five and a half year prison sentence.
The man was not aware that his behaviour would lead to death, found the court.
According to a study reported by broadcaster RTS, up to 20 people are injured and one or two killed each year due to mobile phone use behind the wheel.
Some 40 percent of drivers use their phone when driving, found the study by insurer Allianz.
In Switzerland using a phone behind the wheel incurs a fine of 100 francs.