iPhone iOS 11

On your iPhone go to Settings and scroll down to Accounts & Passwords.

Within that menu click Add Account and select Exchange.

Enter your email address and click Next at the top right of the screen, and if required enter your password for your Office 365 account.

Press Next again and the account setup should complete and you should be able to select whhich items you want to synchronise, Mail allows you to sync your emails.

Click Save.