A simple and easy way to get your Office 365 email on your iPhone or iPad is to install the Microsoft Outlook app.
Here is a guide:
Open the Outlook for iOS app which looks like this:
If you do not have the Outlook iOS app installed, you can download it from the Apple Store here: Outlook iOS App
Note: Available for iOS devices using iOS 10.0 or higher
First time using Outlook for iOS? Just tap Get Started. If not, tap the menu icon the upper left corner.
Type your full email address, then tap Add Account
Note: If you are asked to select your email provider, you may have to set up your email account manually using Exchange or IMAP/POP
Enter your email account password and tap Sign In
Note: The sign in screen may look different for you depending on your email provider
If 2-step verification for Office 365 is enabled, verify yourself using the method you set up (6 digit code, phone call, or using the Microsoft Authenticator app.)
Tap Yes or Allow to give Outlook permission to sync calendar, contacts, etc