Defending the commuting section, as well as possible weekend rides on relatively quieter roads, commuters ride probably on average 9 journeys a week putting up with very heavy traffic carrying a good proportion of people already stressed out headings work or carrying their work stress back home and frequently take it out on or have very low road respect for others - especially cyclists.
Add to this they very frequently use handheld phones knowing it is both illegal and proven as dangerous to do so.
As a regular cycle commuter, I don't as often see how dangerous they are but have many times when driving so if anyone feels they should be grassed up, good for them.
Regarding your opinion that use of a mobile telephone s a lesser crime, they are blatantly in everyones face flouting the law, are fully aware of what they are doing and happy in the knowledge that they will not get a huge fine, lose their license and not be penalised very heavily by their insurance company.
In addition, if a drunk driver causes an accident, it's almost impossible to wriggle out of it, when it's a mobile user, unless here is a witness, video evidence or clear evidence from their mobile records, then they go un- punished in relative terms.
Damn well report them.