Cyclist Dr Dave Brennan recorded the incident on a helmet camera as he tried to persuade the man to put down his phone.
The incident happened in the morning rush hour last month on the A739 Switchback Road between Bearsden and Glasgow.
Mr Brennan told The Scotsman: "I was surprised to see this driver on his mobile phone, especially as he was looking down at it whilst driving.
"I called over to encourage him to stop using it, as it is not safe to drive whilst look at a phone.
"He later started talking to me, and during that conversation claimed he could drive safely when using his mobile phone, which is an astonishing admission.
"He then drove off.
"There is often a queue of traffic on this road, so it was not unexpected for me to catch up with him.
"He'd complained I was previously cycling along at '3mph', so I smiled and waved as I went past, pointing out the fact he was the one now doing 3mph.
"As his window was wound up, I'm not even sure he heard me, but he probably saw me wave.
"He then proceeded to accelerate forward as the traffic ahead of him stopped and he crashed into the car in front.
"I spoke to the two drivers. I offered my footage to the driver in front as evidence, but they decided to settle it between them.
Mr Brennan said he thought the driver had put his phone down after their conversation, and before he crashed.
However, the cycle campaigner has previously highlighted the difficulty of reporting incidents in Scotland.
He has said: “Cameras are absolutely critical – if I had gone to the police in these cases without a camera, it would have been my word against the drivers’.”
In England, a website has been set up by Nextbase to streamline the uploading of such footage.