Get phone to DFU mode. Here is the process.
Entering DFU Mode on iPhone, iPad or iPod touch
Plug your device into your computer with a USB cable.
Turn off the device.
Hold the Power button for 3 seconds.
Hold the Home and Power buttons for 10 seconds.
Release the Power button but keep holding the Home button.
After about 15 seconds you will be alerted by iTunes saying that it has detected a device in Recovery Mode.
Hope this helps. Good luck.