In November, Microsoft released the mobile versions of its applications Office, Word, Excel and Power point for Android, but were only compatible for tablets.
Today, the company released the mobile apps.You can see the announcement from here.
So beta testers can download apps and test them on their mobiles.
To download Office Preview you'll need to enter the Microsoft Office Preview community on Google+ and sign up for the apps you want to try.
You will then be able to download them from the Google Play Store.
Microsoft Office Preview community