How to Add Your Office 365 Email, Calendar, and Contacts to Your iPhone & iPad.
Step 1: Open Settings on your device and then scroll down and tap "Mail, Contacts, Calendars."
Step 2: Tap "Add Account"
Step 3: Tap "Exchange"
Step 4: Enter your full email address and password. You may name the account whatever you like in the description field and then tap Next.
Step 5: Sometimes it will find the mail servers automatically and automatically skip this step. Otherwise you will have to specify Server: outlook.office365.com and leave domain blank. Then enter your full email address into the "Username" field and tap Next/Save.
Finished: Now you may turn on and off which features you would like to sync to your device. Remember that mail, contacts, calendars, and tasks with sync both directions so that the information is the same regardless of what device you are using.