Yes Phyllis is still alive. Why she wasnt on the S1 DVD is a good question. There was a "recent" shot in Gary Grossmans book- but hey
thats already a "few years back".
There was an article on the Superman Homepage claiming that she wants no part of
The Adventures of Superman, that she won't even discuss it anymore. It also claimed that in addition to wanting other acting jobs, she dumped the show because she felt Whitney Ellsworth was selling the show out when he switched over from the B-movie noir approach of Maxwell to the tone of the comic books. The veracity thereof is open to question, but it may explain why she didn't participate in the DVD retrospective.
It wasn't a very old article, maybe a couple years at most. Again, whether it can be believed or not is anyone's guess.