caldav stopped syncing - how to fix without losing entries?
Sorry i dont have enough rep to comment instead. However, if you feel lucky and really really need your calendar events, i would try this:


Backup the iPhone using iTunes to your computer, make sure its a Unencrypted backup.
Navigate to ~/Library/Application\ Support/MobileSync/Backup/
Look for the folder updated recently.
Copy that folder to the desktop.
Start quicklooking through some files from the copy on the desktop, you will find some events (one file is one resource, like contact, calendar event, photo etc)
Sort out the events you need, import them to Calendar again by double-clicking on the event (try one first, make sure you have a backup of your calendar as well)


Best of luck, its a tedious job.