This book contains two chapters of Hinotori ("Firebird"), "Yamato" set about a century after Vol.1 and "Universe", set several hundred years before Vol.2. On the whole, I'd suggest buying this book, but don't give up during the first part.
This story deals with what is left of Yamatai (now Yamato) and Kumaso. As you remember in Dawn both cities were destroyed, Yamatai was inhabited by conquerors from the mainland, and Guzuly's (Emdee) son escaped from the crater and proclaimed that Kumaso would live again. He's still alive, but over a hundred now. The story revolves around Prince Oguna from Yamato who is sent by his father to destroy Kumaso. Despite what you'd think, this story isn't very good at all. Tezuka's humor crosses the line here, clouding the story and making it impossible to take seriously. The singing graves at the end should've been a powerful moment, but the tone of the story made it impossible for me to stop from laughing. Is also doesn't help that there's nothing all that imaginative or interesting about the plot. Dawn and Future were far better stories.
Now here's a surprise. I've been lead to believe that the stories set in the future aren't all that good. Hinotori is, after all known for stories such as Dawn and Ho-o, wonderful stories set in Japan's past. So imagine my surprise at finding Universe to not only be better than Yamato (no impressive feat, that) but it also managed to live up to the reputation that Hinotori has earned over the years. It's easily as good as Dawn or Future. The story takes place a few hundred years before Future. At this time, humanity is still spreading across the stars. The great contraction hasn't yet taken place. One character from Future is present though, a much younger version of Saruta. The story is about Hell, I suppose. Like Dante's version of Hell, there is no sense of hope at all in the pages of this story. The characters are doomed to spend their lives alone in the conquest of space, to outlive their families. Then when they eject from their damaged craft, there's very little hope that they'll be saved or ever see Earth again. Then they eventually do get to a planet, which is quite literally Hell (though we wouldn't recognize it at first, since it's far more subtle than Dante's variation). This is a very dark chapter of Phoenix, even moreso than Future (though you probably didn't think it possible). If western readers have felt disconnected from the Buddhist worldview present in Future, they'll find themselves much more at home here, I think.
As I said before, the book is worth buying simply for Universe alone, so don't let Yamato get you down. The best part of this is, oddly enough, that by releasing both of these stories at once, Viz has pushed forward the release date of "Ho-o" (Karma) considerably. Look forward to that, folks, considered by many to be the best episode of the series, one of the best manga ever written.