Open Outlook on your PC
Sign in to the same Microsoft account used on your iPhone
Make sure your Outlook calendar is saved in Outlook.com or Microsoft 365, not only stored locally on the PC
On your iPhone, open Settings
Tap Calendar
Tap Accounts
Tap Add Account
Tap Outlook.com or Microsoft Exchange
Sign in with the same account used in Outlook on your PC
Turn on Calendar sync
Open the Calendar app on your iPhone
Check that the Outlook calendar appears
If using the Outlook app on iPhone, install it from the App Store
Sign in to the Outlook app with the same account
Enable calendar permissions in iPhone Settings for the Outlook app
In Outlook on PC, ensure the calendar is selected and syncing to the cloud
If needed, refresh the Calendar app on iPhone
If sync does not appear, remove the account from iPhone and add it again
Keep Outlook and iPhone updated to the latest versions