In order to play on the phone or tablet with Android on Unity, you must install one of two browsers:
Puffin Web Browser
Photon Flash Player & Browser (not checked)
These browsers are best suited for the game The Settlers Online (free versions of browserss display ads).
This is currently the only option for playing The Settlers Online, because there is no dedicated game application and it will never be.
Browsers are available for Android 4.1 and newer.
You can find all the information on the client wiki HERE