Be careful attacking the character of the officer unless you are sure taht they are dishonest, and have proof to back it up.
If you call their character into question, your character will also automatically be called into question, and any previous convictions or matters of dishonesty can be laid in front of the court.
I appreciate the costs involved, but if you are thinking of attacking procedure or character, you really do need experienced representation, or you risk being made to look like an absolute fool, or worse an absolutely dishonest fool. At the same time, if the officer is of good character, this will have to be acknowledge and placed on record by the court. The courts have seen it all before - and the CPS Rep - however inexperienced (or
not - some are fantastic) will wipe the floor with you if you start trying to "play the system".
Just fight it on fact - if you weren't using your phone, then phone records and the other facts will prove this.