Based on the AOSP Softkeyboard Example from Google. Vowels, Virama, Conjunct Consonants are all handled automatically.
Installation Instructions, follow here:
http://www.partha.eu/partha/installing-the-sanskrit-phonetic-transliteration-keyboard/
or you can google for "how to add a new keyboard to android phone" see For e.g:
https://www.androidcentral.com/how-set-default-keyboard-your-android-phone