Phoenix(1956) is split up into three arcs. I feel like each of them deserve individual scoring which will be averaged to get my final ratings. This review will be as spoiler-free as possible.

Egypt Arc:
Story: 8
A look at an Egyptian power struggle with the Phoenix shaping history. This arc easily had the most compelling story.
Art: 7
Tezuka has his unique art style that is used throughout all of his works. This one doesn't stand out so I give it my default art rating.
Character: 7
This is the only arc where the main characters get much development. They are good but nothing special even here.
Enjoyment: 8
Didn't have the overall impact Tezuka's works usually do but it was a fun tale nonetheless.

Greece Arc:
Story: 7
The Trojan horse story(overused) in which Daia and Krav play a crucial role that is a pretty good read
Art: 7
Same as Egypt
Character: 6
After the first arc, the main characters reset and end up basically defaulting to the same characters in the first arc
Enjoyment: 8
This arc should have had an original story like the other two but it was the longest and had some good moments.

Rome Arc:
Story: 7
A very basic but kinda cool Roman story that didn't make much sense.
Art: 7
Same as Greece
Character: 6
The main characters reset again and don't really get much focus.
Enjoyment: 7
Seemed like there should have been more time put into this one but it was pretty fun

Manga Overall:
Story: 7
The stories, when read together, paint a picture of the lives of Daia, Krav and Chirol.
Art: 7
Art isn't something I almost ever care about. I will give it a 7 if I don't find things I hate or love about it.
Character: 6
The characters just didn't get enough focus outside of the first arc and they weren't much to brag about even then.
Enjoyment: 8
This is a fun trip through history. Not nearly as thought-provoking as most Tezuka works. Maybe if it got finished, it would have been.

Being unfinished, this story has a huge hole in it as far as closure goes. The characters are too pushed aside to be really good. Bottom line: This manga needed more chapters.