Hi Steve
Just been through a similar case and was lucky to be aquitted. Basically it was down to the word of the Garda against my word, and (my trump card, as the judge said) my partners.
As has been pointed out, the offence is holding a phone so all phone records are "irrelevant", though they did in my case show that I infrequently used the phone, which was noted.
I did have a solicitor, and he made sure that both of us got to give evidence. I tended to elaborate on what had occoured on the day (things like, the phone was stuck in my pocket and I didnt realise I had it, etc) and the judge mentioned that this made it seem like I had something to hide.
Basically just say, and repeat, "I was not holding a phone" and answer any questions asked. It is then up to the judge to decide who is telling the truth.
One thing that helped my case is that the Garda stated, in his evidence, that he only observed me as I passed him, in other words, only momenteraly, as opposed to seeing me as I approached. This is where the solicitor will be usefull in picking up on these details.
The alternative, which some people used successfully (Im not claiming that it was not true), is to swear that you never received the origional Notification of the Offence, due to some addressing fault.
Finally, it did cost a days holiday for myself and my partner plus a bill from the solicitor that was far more than any fine or insurance loading. However I am happy to say I still have a points free license (for now).
Good luck