Adding an Office 365 mailbox to an iPhone is an almost identical process to configuring one to work with Exchange Server 2010—the only difference being that the server name provided as part of the Auto Discover process isn't likely to be one you already knew.
To manually add our test mailbox, navigate on the iOS device to Settings, then choose Add Account..., selecting the Microsoft Exchange option.
On the screen that follows, we will enter the same settings used in the Remote Connectivity Analyzer; the e-mail address, the Microsoft Online Services ID (typically the same), and the password. Then, tap Next:
The iOS device will now attempt to complete the Auto Discover process, and after a few moments should display a server name under the outlook.com
domain:
We'll then choose Next, and save the settings to the device. After a few moments we should see the contents of the mailbox in the Mail application:
As with the Outlook Web App test, it's worth verifying...