There is some really helpful documentation available on how to set up your CSU email on your phone. Look at this section:

Connect your Mobile Device to your Office 365 Account

- Configure an Android Device to connect to Office 365

- Configure an iPhone or iPad to connect to Office 365

I don't believe that you need to install Outlook unless you want to keep the mail in a separate application.

Please let us know if you're still having troubles after following the instructions linked above.

Thank you!