So you have downloaded the book.
I recommended you to read it with your iPad. Of course you can read it with your iPhone.
Firstly, do not unzip the files.
Download an apps that can read aozora bunko format files.
You can search with the term "aozora".
I use the apps called iBunko HD (for iPad). It's not a free apps.
Follow the instruction given with the apps to view the files.
The apps will read the zip file and you can enjoy your reading.
