For this setup to work your phone must be on IOS 11 or later as of 2022. Usually that means your iPhone must be an iPhone 6 or newer.
https://support.microsoft.com/en-us/office/system-requirements-and-supported-accounts-46a8d501-0d1f-4145-ab0f-286bc7dcf780
https://support.apple.com/guide/deployment/integrate-with-microsoft-exchange-dep158966b23/web