Q: why can i no longer add a location to a calendar event

Howdy harrisfennell,

If you're not seeing the 'Location' field when adding an event in Calendar on your iPhone it may help to force close all open apps and restart the device.

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 the Location field is still missing when adding an event in Calendar, 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

All my best.