I was driving back home yesterday from picking up the eldest from Saturday job and saw a guy on a nice road bike, all the gear on ,he was riding one handed, on the drops,slowly, and dialing on his mobile phone ,behind him he had a queue of about 20 cars, that sort of behaviour just pees people off, why not just stop and make the call ?.
This is poor behaviour, whether illegal or not.
Dialling on a hand-held device while cycling in front of a long queue of traffic shows discourtesy.
Even if he hadn't slowed down to use the hand-held device, he may have given the impression that he had.
The OP is right to question this. We all have to share the roads.