Taken from here: https://github.com/aws/aws-sdk-php/blob/master/README.md#installing-via-pear
Installing via PEAR
PEAR, which stands for PHP Extension and Application Repository, is a framework and distribution system for reusable PHP components. It is the PHP equivalent of other package management solutions like Yum that install packages system-wide.
PEAR packages are easy to install, and are available in your PHP environment path so that they are accessible to any PHP project. PEAR packages are not specific to your project, but rather to the machine they're installed on.
From the command-line, you can install the SDK with PEAR as follows. Note: You may need to use sudo for the following command.
pear -D auto_discover=1 install pear.amazonwebservices.com/sdk
Once the SDK has been installed via PEAR, you can load the phar into your project with:
require 'AWSSDKforPHP/aws.phar';