Lompoc has an inmate that is a party to a California divorce action. Trial is set. Can he appear at the trial via telephone per judge's order?

Highly unlikely any judge would require a federal inmate be present at a divorce trial. If the judge wants to hear from the inmate, it would be a telephonic communication request. The BOP is known to allow inmates, as a party to a civil lawsuit, make a call(s) to their lawyer to convey how they would like to be represented.