Requirements to set up Live bootable USB
Your Andriod phone can be turned into a Live bootable USB using Drive Droid app. It is free utility app using it you can boot directly into Linux. Your phone can be turned into a Live USB only if it has following requirements.
In the phone:
1. Rooted Android phone
2. Memory card or phone storage with minimum 2 GB space.
3. Wi-Fi connectivity (To download OS in your phone)
4. USB cable
1. USB port
2. Minimum disk space 30 GB
3. Minimum requirement of specific Linux distro - 512 MB RAM, x86 architect processor (normal processor that came in-built with your laptop).
This app uses a lot of resources from your phone and I recommend you close all the apps before launching DriveDroid app. Connect headset to your phone, suppose if you get a call attend through it which won't disrupt the set up. Only challenge you face is rooting your phone. Read articles on how to root Android phones.
Steps for booting Linux OS from your Android phone
You can run Linux OS directly from your phone without installing it in your computer. Our first aim is to run Linux OS from Android phone. Later I will explain steps involved in installing. It is just like using your phone as a OS CD.
1. You first need to set up DriveDroid app. Just launch the app and follow the initial steps. These steps can be done easily by the notes given in the app.
2. For this step you need internet connection. Connect your phone to your Wi-Fi connection. In this step you will be asked to download a Linux distro image. Download any Linux distro of your choice. If you are new to Linux then choose Ubuntu to which I have given complete installation guide. It will take few hours depending on your network speed.
3. After your download gets completed you can use that image to boot your PC. Now you are going to use this image to boot Linux OS in your computer. Connect your phone to computer via USB cable. Select the downloaded image from the DriveDroid. You can select it from the main screen. Once you select the image it will ask for Writable USB or Read-Only USB. If you want to install the OS in computer then choose Writable USB or if you want just run the OS without physically installing it in you computer choose Read-only USB.
4. Turn on your computer and make USB as primary boot. To set USB as primary boot, press F2 or F10 key to enter BIOS screen. There in boot tab set 'Removable Dev' as 1st boot disk. Then restart your computer and make sure your phone is connected to the computer. Now it will directly boot into Linux OS.
You can install any Linux OS by running the Live installer found in the desktop of Live OS. Double click on the Live installer and give the password as Root. Installation will be started and just read the instructions to move on. For installing Ubuntu Gnu/Linux, read this article.
Very good and useful guide with complete details. Will help many who are interested to try using Linux on the Android phone.