iPhone user can't connect to Exchange 2013 via iOS Mail app
says "Unable to verify account information" on the phone.
Delete Account for O365
Make sure the user is not using WIFI / Turn off WIFI
Bring up Safari and connect to http://outlook.office365.com
Make sure you can logon with credentials successfully.
Now set up the O365 Account in IOS Email.
Server Account: outlook.office365.com
You may have to uncheck SSL and then recheck SSL
Now you should be able to logon and start receiving emails.
Turn WIFI back on.