Empress of the Deep 3 Legacy of the Phoenix is the newest in a line of adventure games from Big Fish Games that, while finely crafted, has a hard time on the iPhone's smaller screen. The depth and detail involved make it tough to fully engage with the number of options onscreen, text is small and hard to read, and hitting the right space is often difficult.
These things don't detract from what is otherwise a very enjoyable adventure game; but if you have an iPad, you will probably better enjoy the game on the larger screen on which controls operate more efficiently. That said, the game, itself, is a fine example of visual storytelling, combining fantasy elements of numerous cultures with a twisting and turning story of an empress out to find her lost tribe and save them from her evil twin. While the story doesn't make a lot of sense at first, it unfolds nicely, and playing the first two games in sequence will help you get a better grasp of the story, although it is not required.
Empress of the Deep 3 is a great game in many ways, but it is not best suited for the small screen of the iPhone. If small text and smaller touch spaces don't bother you, then the game will play just fine, but if you are eager for the full experience, the iPad version is a better fit.