To set up your email on an iPhone, simply follow the below steps.
Go to your iPhone or Apple Devices settings, scroll down and click on Accounts and passwords. Then press Add Account.
Once you are on that screen, click on the Exchange icon.
Enter your Office 365 email and description of your account and then type sign in.
Enter the password of that email account and tap Sign in.
The Mail app may request certain permissions to access your mailboxes or sign you in and ready your profile, accept those permissions.
Finally, choose the services you want to sync with your iOS device and tap Save.
And your email will be all set up!