Launch the instance and connect with ssh.
##Update the server
sudo yum update
##Install php and MySQL packages
sudo yum install https mod_ssl mysql mysql-server php php-mysql php-xml
##Install phpMyAdmin
Get the RPMforge repo (32-bit, for 64-bit use http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.2-2.el5.rf.i386.rpm)
wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.3.6-1.el5.rf.i386.rpm
sudo rpm -Uvh rpmforge-release-0.3.6-1.el5.rf.i386.rpm
Install
sudo yum install phpmyadmin
##Start MySQL service
cd /etc/rc.d/init.d/
sudo ./mysqld start
sudo /usr/bin/mysql_secure_installation //follow instructions
##Setup startup scripts for apache and MySQL
cd /etc/rc.d/rc3.d
sudo rm K15httpd
sudo rm K36mysqld
sudo ln -s ../init.d/mysqld S30mysql
sudo ln -s ../init.d/httpd S85httpd
##Setup phpMyAdmin
Allow access from external IP's
sudo chmod 0700 /etc/httpd/conf.d/phpmyadmin.conf
sudo nano /etc/httpd/conf.d/phpmyadmin.conf
# Web application to manage MySQL
# #
# Order Deny,Allow
# Deny from all
Allow from 127.0.0.1
#
Alias /phpmyadmin /usr/share/phpmyadmin
Alias /phpMyAdmin /usr/share/phpmyadmin
Alias /mysqladmin /usr/share/phpmyadmin
Set blowfish_secret to make it work with cookie auth
sudo chmod 0700 /usr/share/phpmyadmin/config.inc.php
sudo nano /usr/share/phpmyadmin/config.inc.php
...
$cfg['blowfish_secret'] = 'put-a-magic-string-here'; /* YOU MUST FILL IN THIS FOR COOKIE AUTH! */
...
sudo chmod 0755 /usr/share/phpmyadmin/config.inc.php
##Make mod_rewrite (.htaccess) work in subdirectories
cd /etc/httpd/conf
sudo nano httpd.conf
Find <Directory "/var/www/html">
Replace AllowOverride none
with AllowOverride all
(optional if apache is running already, restart it)
sudo service httpd restart
##Start apache
sudo /etc/rc.d/init.d/httpd start
##Sources
Here's a nice Blowfish Phrase Generator