Legal Question in Family Law in California

You can show whatever you want but if the phone was in your ex 's name and there was no court order that the ex provide you phone service I wouldn't expect the judge to do much.

The court will likely not care about this. The judicial officer will likely tell both individuals that they need to work with one another and to put the needs of the children first. The worst case is the Judge/Commissioner may think you are being trivial. Often the time to bring these small things up are to the mediator if you are in a recommending county.