My Kindle 7 HDX does not pick up calendar entries from my iphone, it used to but now it doesn't. Any ideas?

This is most likely an issue with the calendar program you are using as the iPhone and Kindle do not specifically communicate with each other. What calendar program are you using (e.g. Gmail, Yahoo, Outlook, etc.)? Check on that calendar and make sure that your iPhone events show up on that calendar. If they do, then you have an issue with the calendar sending to your Kindle. If not, check your calendar settings on the iPhone to make sure the calendar syncing is turned on.