Syncing Outlook 365 to iPhone

I am running Windows 10, and using Outlook 365, which I used to regularly sync with my iPhone using iTunes.  I have never worked with the Cloud storage for Outlook, always working with my local PST file.  Recently my iTunes refused to sync with my local Outlook file, and after trying to resolve the problem it appears as though I should be switching to the Cloud for my Outlook and the syncing.  But when I went to my iCloud settings to tell it to backup my Outlook, I got the following error message - with no instructions for how to set up Outlook for the "default profile".  I don't want to lose my perfectly functioning Outlook email, Contacts, and Calendar.  Please advise.



Thanks,

Phil