I use Office365 and have managed to get Outlook 2016 calendar to post and sync to iCloud to my iPad and iPhone but it doesn’t sync the other way. e.g., if I add an appointment on the iPhone it does not sync back or show on the outlook (icloud). What am I missing?
You can try removing and reconfiguring your Outlook settings first.
If you’re still having issues check your phone settings, and make sure it’s not syncing to iCloud. If it’s turn it off, the open iTunes, and see if there is a new option to sync to Outlook.