How to text in Japanese on iPhone

It's a little bit complicated.

After you type any character or word, you need to double tap done button.
VoiceOver reads "kakutei".
It's the right key of number 7, same as "kaigyou", the button for new line.
In this way, you can input all letters in hiragana.

Before double tap kakutei button, some candidates appears on the place above the number 1-2-3.
You can check it by right and left flick, or up and down flick.
When you find the proper candidate, double tap on it.

Well, there are two other ways to show candidates of kanji.

The right key of number 6, it is the button for next candidate.
When you find the proper candidate, double tap on it.

After you type letters, you can do one finger up and down flick.
You can check candidates.
If it does not work well, you need to set the auto-text mode by rotor gesture.
Normally, it sets auto-text mode automatically.
When you find the proper candidate, double tap on it.