1. Go to Settings > Calendar

2. Click Accounts

3. Click Add Account

4. Add CalDAV Account

5. Fill up the details

6. Click Continue

7. Click Save

8. Go to Calendars and you will see your calendar under your domain.

9. Go to your webmail > Calendar > Create new event

Once created, click Save.

10. On your Iphone, it will sync with a server.