Here is a guide on how to setup a Microsoft Office 365 email account on an iPhone or iPad using the iOS Mail app.
STEP 1. Go to Settings > Accounts & Passwords > Add Account
Note: If you’re on iOS 10, go to Mail > Accounts > Add Account
STEP 2. Select Exchange
STEP 3. Enter your Office 365, Exchange, or Outlook.com email address and a description of your account. Then tap Next
STEP 4. Tap Sign In
Note: Tap Configure manually if you need to enter server settings
STEP 5. Enter the password that you have been provided with your email account. Then tap Sign in or Next
STEP 6. Choose the services you want to sync with your iOS device and tap Save. You’re done!
For the best experience, you can use the Outlook for iOS mobile app