By default on a brand new iPhone, when you double press the home button it will take you to your phone favorites. This was true until iOS introduced multitasking. Now when you double click the home button on your iOS device to open the recently use apps. Here you can quickly switch to other apps without going to the home screen. If you want to read more about multitasking in iOS click this link. Even though the home buttons double click has changed you can still change it in iOS. Here is how to change the double click home button on the iPhone.
Change the Double Click Home Button
The first thing you need to do is go to the Settings icon. You can find it on your homescreen, looks like gears, and press it.
The Settings app will open. In the Settings app, scroll down until you see the General menu option. Press it.
In the General menu press the Home menu option to go to the Home settings.
This is where you can change what happens when you double click the home button. I set mine for the camera.
Every time I double press the home button it will open the camera.
You can change yours to whatever you like. Or just leave it as the default. Whatever decision you make you can always go back to the settings and change them. What do you have your double-click home button set to? Any specific settings?