Hi there, I´m Ivania. I´m an Independent Advisor and a Microsoft user like you. I´ll be glad to help you today.
So sorry about that, it usually happens when your phone has been upgraded to a new version.
Apparently this occurs when the Outlook App is pushed from your device manager.
Please delete the app again, power cycling your iphone, and download it again from the App Store. After siging back in, test to your self.
see more in the discussion forum:
https://answers.microsoft.com/en-us/msoffice/fo... 1
Best Regards