If you have outlook contacts saved onto your iPhone, make sure to import these contact BEFORE removing the account from the settings
Settings > Contacts > Import Contacts > Select Email account.
Once Outlook is configured, Follow the steps below to re-sync Outlook contacts on IOS:
1. Open Outlook on your iPhone.
2. Tap on your user profile image on the Top-Left.
3. This will bring you to the app settings, Select your Office 365 Account.
4. Turn on the Option to save Contacts.