When you have a problem with your iPhone, the exchange calendar not syncing with iPhone. Sometimes it happens due to misconfiguration on your iPhone.
It can be quickly determined by syncing your exchange server on other phones.
If the other phones don't have any synchronization issue, then the problem is with your iPhone.
Because, on iPhone’s, iCloud calendar will be the default option. So if you would have created an event, it will be saved to iCloud instead of Exchange. Scroll down this page to solve exchange calendar not syncing with iPhone issue.
If the method mentioned above is done and still Exchange calendar is not syncing with your iPhone, then check Outlook Web App for the events you have added. If it is visible, then go to your iPhone Settings and perform the steps mentioned below:
Check if the calendar event added in OWA syncs with your iPhone. If yes, then remove your iPhone in OWA.
Log in to Outlook on the web.
Go to Settings and then select View all other settings followed by General.
Select the Mobile devices option.
Select your phone and then click the delete icon.
Finally, click Save.
After removing your iPhone from OWA, you have to completely power off it.
Configure Exchange Account on iPhone
However, sometimes you need to set up an Exchange account on your iPhone to resolve the issue.
On your iPhone, go to Settings.
Select the Mail, Contacts, Calendars option.
Choose the Add a new account option.
Click on Exchange.
Enter the email address, password, and description to add your account and tap Next.
Now, enable syncing mail, contacts, calendars, reminders, and notes.
Finally, it will sync all of your contacts, calendars, tasks, reminders, and notes with your iPhone automatically.