Q: I have a i6 but it is not showing my caller id

Hi Vijay,

It sounds like you can see the option to turn on Caller ID but it is grayed out and you cannot toggle it. You may need to reach out to your about it according to the following article:

 From: Call forwarding, call waiting, and other call features on iPhone

https://support.apple.com/en-us/HT202176

                      

Caller ID

Turn on or off in    Settings > Phone.

Contact your carrier for information on using Caller ID.

Just to cover all the bases you can try troubleshooting the software to see if this is an issue w can resolve. Start by quitting the Phone and the Settings apps:

Force an app to close in iOS
https://support.apple.com/en-us/HT201330

1. Press the Home button two times quickly. You'll see small previews of your recently used apps.
2. Swipe left to find the app you want to close.
3. Swipe up on the app's preview to close it.

 
When you have done that restart the device and test the issue again:

iOS: Turning off and on (restarting) and resetting
http://support.apple.com/en-us/HT201559
 
If the issue persists, backup your device to iTunes, then restore it as new and verify that it works. 
 
How to erase your iOS device and then set it up as a new device or restore it from backupshttps://support.apple.com/en-us/HT204686

If it does, then restore your backup to either verify it still works and the software just needed reinstalled, or isolate the issue to the backup file itself. 

Thank you for using Apple Support Communities.