E-SAKUGA would appear different on iPhone and iPad.

Since June 2015, iPhone supports Apple Books Author format in Apple Books. 
Due to this change, E-SAKUGA became available on iPhone. Various features including Tapmation™ are 100% intact. However, due to Apple’s specifications, how Apple Books Author books appear/work on iPhone is different from iPad. 

Each action is performed in a separate window for iPhone, so E-SAKUGA’s seamless operation between checking the key frames, time sheets, and reference videos simultaneously  cannot be done in iPhone. Please have this in mind if you intend to view E-SAKUGA with your iPhone.

Added on October 2016:

Since iOS10, Tapmation™ works as intended also on iPhone.

Tapmation™ does not open a new window anymore and works seamlessly like on an iPad.
However, still images will prompt a new window like before. We cannot view all elements on one screen seamlessly like on an iPad.

Sample Image of E-SAKUGA on iPhone

The still image in iPad is operable by just tapping the screen, but on iPhone each element operates on a different window. Thus, we cannot see the time sheet and key frames together.