Q: find my phone

You can't find the iphone because.....  ???  It's offline?  It's not listed as a device?  You can't log into icloud?

If offline, then it could be disconnected from the internet, it could be turned off, it's battery could be drained.

In order for a device to be tracked, it must have the Find My iPhone service turned on in Settings>icloud.  The Find My iPhone app has nothing to do with this, it is only an app that you use to find other lost devices.

If you have not turned on the service, then you can't locate the device.  If you did, then log into icloud.com with a browser (or use Find My iPhone app with another device) and go to the Find My iPhone page.  There you can track registered devices.