If you have already opted in to Two-Step Login for Office 365, authenticate using Two-Step Login.
Recommended: If you are concerned, use the Microsoft Outlook App for iOS instead. When configuring a Cornell Exchange account on your iPhone, you may see a warning that 'Adding an Exchange account will allow the Exchange administrator to remotely manage your device. The administrator may collect personal data, add/remove accounts and restrictions, list, install, and manage apps, and remotely erase data on your device.' Learn more about what this means.