Defending in a case like that is difficult because it is not one or two witnesses who really 'tell the tale', give the key evidence. You can cast doubt on them and there's a result. In this case the evidence is circumstantial. It is not one witness giving the whole picture, but lots of witnesses, and lots of documents, each giving a tiny bit of evidence, not damning in itself, but which taken together amount to proving guilt; you haven't got the pretty picture on the box, you have the 1000 piece jigsaw that makes it !
So your only line is to attack and remove some of the pieces. Then you have to say that what is left is not enough and keep reminding the jury of the bits that are missing, ignoring the rest. Unfortunately, you find that a lot of the time the jury have got the picture in spite of the missing bits!
But if the witness to doing his phone doesn't come up to proof , say what is expected, or is discredited, that defendant's case is up and running, because it seems so important to the prosecution that they dared open it.