What is phone bricking? bricking means making a phone unusable, that is handset will absolutely refuse to boot at the press of the power button or boot and stop at device welcome logo (hanging) but you sure your battery is not faulty at this state your phone is as useful as a brick


Types of Bricking
Soft Bricking: At this stage the phone boots and hang at the welcome logo this type of bricking can be easily recovered if done early enough
Hard bricking: Phone refuses to power on, this stage is usually hard because most time the phone is considered dead and can be recovered using jtag. You can take it to any mobile phone engineer for assistance

Causes of bricking
Rooting of Phone: this can happen when root process is interrupted or not following the instruction given on the rooting app.
Use of Fonts:this is number one culprit to Android bricking.S when ever you changing or tweaking your phone look make sure you have rooted your phone properly and have good backup.
Flashing of ROM: Before you make changes on your phone ROM please ask questions to know if the new ROM to be installed is main for your phone.
System Update without properly Unrooting phone.
Failing to clear/wipe the data/cache:This can cause Android to go into a bootloop because of the mismatches with the Android's virtual machine and the apps installed, or more than likely, a corrupted dalvik cache.

How To Avoid Phone Bricking
First you must avoid the above listed causes of bricking.
if you must tweak your phone or change the phont style make sure you have at least 55% battery level to avoid power interruption during the installation process
Also if you must do system update for your android device allow the phone to request for system update before updating why? because you may wipe off the current Android operating system there by installing unsupported operating system for the device so your phone wont boot.
Always try and to clear your [hone cache memory to avoid low memory you can also delete thumbnails from your device manger (this thumbnails are created in phone memory when ever you play and pause movies on your phone).
http://www.getontopc.com/2016/09/what-is-android-brickingcauses-and-how.html?m=1