Can you turn on the phone? If you can't turn on the phone, there is nothing you can do to erase it.
If you can turn on the phone, follow these directions:
If the phone is still seen through USB connection and sounds, try using DFU mode, and a computer with iTunes installed. To do this...
1: Install iTunes to a computer (if it's a Mac, make sure iTunes is updated).
2: Connect the USB cable between the iPhone, and the computer.
3: Hold down the Power button and the Home button for approximately 30 seconds. If the phone is functional, the computer should detect the iPhone as in recovery mode.
4: When iTunes prompts, hit the "Restore" button
5: Allow time for iTunes to download the latest iOS Image. This will be a file approximately 1-2GB big. If you have a very slow Internet connection, give it some time.
6: iTunes will erase the phone, re-install the software, and then reboot the phone.
If you can do the above, your data will not be recoverable. All modern iPhones are encrypted, and the method above destroys the key to your data on the phone. It's as good as blank.
Should you have a very slow Internet connection, the iPhone may leave recovery mode while iTunes is downloading a fresh copy of iOS, and iTunes may throw an error about restoring the phone. If this happens, press and hold power and home buttons again for 30 seconds, until the phone re-enters recovery. Then, iTunes should use the already-downloaded image to restore the phone.
If you plan to sell or repair the phone, and iTunes asks for an Apple ID/Password to unlock the phone after it is done restoring, please enter your credentials. This removes the activation lock so you don't have an upset customer / fees from Verizon / etc.
Hope this helps!
As another note, if the phone is not able to be restored because it is totally dead, you have two options.
1: Take it to Apple for repair/destruction
2: Request electronic recycling to remove the battery, and securely shred the phone using an industrial shredder.