I'm not sure if this thread is driven by defence of breaking the law or antipathy between cyclists and drivers.
However, the long and short of it is using your phone in a car that's not parked up is illegal. There is no real argument. There are no shades of grey, it's black and white. I can't think of any other law where people would so vigorously defend breaking it.
'It's ok m'lud, he was pissed as fart behind the wheel of car, but it was stopped at traffic lights'. Well that's ok then.
'Your honour, she was 15 but mature for her age, so no harm done.' Good on you mate. You're not really a nonce.
There are reasons that you have blanket laws with defined parameters.
The truth is, if you don't want to be pulled up by others or the police, don't break the law. If you are checking your phone whilst the car isn't parked up, you're a shit driver. No ifs or buts, you are as bad as the twat who speeds or one that can't parallel park.
You're a shit driver with no defence.