caldav stopped syncing - how to fix without losing entries?

My family uses caldav in their iPhones to keep a shared calendar (yahoo) in sync with everyone. One phone, used to add a lot of calendar entries, has stopped syncing. I tried simply reentering the PW to see if that would jump start it, but it is still "stuck". With no diagnostic information available, I don't have a clue why. If I "delete" this shared calendar, I will lose calendar entries added to the phone but not yet at the server. Any suggestions? Is there an easy way to select all calendar entries for a calendar and perhaps move them to the "local" calendar, Then I can delete the shared calendar, add it again, then move those new entries back to the shared calendar? I wish there were some way to diagnose and fix this, I just don't think Apple has ever provided any tools for that.