Why does iTunes show more home screens than my iPhone?

My iPhone 6 has two home screens. When i connect to iTunes it shows three home screens.

When you connect your device to your computer and allow it to be recognized by iTunes, it automatically goes into an edit mode. This allows you to alter your device's home screens via iTunes. It's the same as if you were to tap and hold on an app's icon until all of them begin to jiggle, causing it to have an additional homescreen.