Outlook can only sync Calendars with Android How do I sync my Outlook Calendar to the default Calendar app(s)? – Microsoft Support

the only workarounds I can recommend for this :

1. Share your work calendar to your iPhone account from Outlook and added it to your iPhone Calendar as a subscription. Don’t set it up as a calendar/account. Subscriptions are read-only, but easy to edit in Outlook app when needed.
2. You fully enroll your Personal Device into PA intune ( Not recommended as we have full control over the device ) which drops the restrictions because we can protect the whole device instead of the app.