Q: Calander doesnt work on ios 9.3.1, iphone 5

Hi batmanas,

I understand that the Calendars app is quitting unexpectedly on your iPhone. Fortunately there are a few additional steps that may help stabilize this app.

Force an app to close in iOS
http://support.apple.com/en-us/HT5137

Turn your iOS device off and on (restart) and reset
http://support.apple.com/en-us/HT1430

If Calendars continues to quit unexpectedly, the next step would be to reinstall iOS on your device by placing it in Recovery Mode, then choosing Update in iTunes. Prior to doing so, it's always a good idea to make sure that you've got a backup made.

1. Make sure that you have iTunes 12 or later on your computer.
2. Put your device in recovery mode.
3. When you get the option to restore or update, select Update. This will reinstall iOS without erasing your data.

If your iPhone, iPad, or iPod touch doesn't respond or doesn't turn on
https://support.apple.com/en-us/HT201412

Cheers!