These are the instructions to root Amazon Fire Phone smartphone using the KingRoot Application on the mobile itself (no need of computer).
Requirements: Your smartphone should have at least 20 percent of device battery or more to begin the root process.
Step 1: On your Android Device, Open Settings > Security > Device Administration > Unknown Source (tick to enable it).
Step 2: Download and install KingRoot APK on your Android Device.
Step 3: Once Installation is completed, you will be able to see the following icon in the Launcher Menu:
Step 4: Tap on the KingRoot Icon to Open it. Once KingRoot Application is launched you will be able to see the following screen:
Step 5: Now, Tap on the Start Root Button to begin the root process.
Step 6: Within a minute or two you will be able to see the Big Green Tick, which signifies that your device is rooted successfully.
Step 7: Restart your Android Device.
Step 8: Now, you can replace the KingUser and other chinese application with SuperSU (chainfire). To replace, follow how to replace KingUser with SuperSU.
[*] The above method tested on Amazon Fire Phone (running on Amazon Fire OS v3.5) without having any issues.
[*] Powerful Tool: KingRoot is a very powerful tool, that allows you to root Android Devices from 2.3 to 5.0 without any issues.
[*] No data loss process: Your Phone Data like contacts, pictures, videos, music and etc will be not affected with this method.
[*] Warranty Void: Your Phone Device Warranty may be Void after following the above tutorial.
[*] Amazon Stock Firmware: If you are looking for the original firmware for your device then head over to Download Amazon Stock Firmware for all devices page.
[*] Amazon USB Driver: If you are looking for the original USB Driver for your device then head over to Download Amazon USB Driver for all devices page.
[*] Credits: KingRoot Application is created by Kingroot Studio. So Full Credits goes to them for the Application.