First off, thanks to several fellow birders who made suggestions on what to do about the black phoebe nest.
A volunteer from Pacific Wildlife Care came to the house and removed the dead adult and one dead chick from the nest. One live chick remained, and he took it with him to PW's center to be rescued. The other adult phoebe was not to be seen. PW suggested that the bird may have ingested pesticide, perhaps from an insect.
Sad, but at least one of the little ones has a chance. We're very lucky to have Pacific Wildlife.