How to Prevent Duplicates When Syncing Outlook?

When syncing Outlook and iPhone with the app, make sure that you first turn off the "Save Contacts" setting  in your device's Outlook app, as detailed in the article below. Otherwise, duplicate contacts will likely result.

https://support.microsoft.com/en-us/office/how-do-i-save-my-outlook-contacts-to-my-ios-contacts-app-51b8450f-2f07-41ab-96ea-afc0de7e6529