On whatever device you are adding an Office365 account to,you will add it as an 'Exchange' account.
You will need your email address and password.
When asked how you would like to connect,(between Configure Manually and Sign In),Choose 'Sign In'
Sometimes you will need the following:
Internal Server : outlook.office365.com
External Server : outlook.office365.com
SMTP Server : smtp.office365.com
Click here for directions to setup your iPhone.