You can't. Your iPhone recognizes the apple TV on the network, not the apple TV seeing your iPhone.
1. Make sure the apple TV and your iPhone are logged into the same network.
2. Close and reopen any applications on the iphone you want to use your apple TV with (ie music, videos,YouTube), and you may want to restart the iPhone.
3. When they are on the same network you should see the rectangle with the superimposed triangle pointed up accross the bottom when you have airplay ability. Hope this helps.