Comment 1 for bug 852804

Yes, this is related to the PHP being pegged at 5.2.

You can remove that pegging and go to 5.3 and install PHPMyAdmin by:

sudo rm /etc/apt/preferences.d/php
sudo apt-get update
sudo apt-get install phpmyadmin

But you'll also need to go through some more config re-integrating MYSQL.

Below are my notes.
----
#SETUP MYSQL PASSWORD
/usr/bin/mysqladmin -u phpmyadmin password 'yourpaas'

#REMOVE PEGED SOURCES, UPDATE, INSTALL PHPMYADMIN
#Pantheon pegged the system to a specific version of 5.2, making it impossible to install phpmyadmin
#Note that this WILL take us to 5.3 PHP
sudo rm /etc/apt/preferences.d/php
sudo apt-get update
sudo apt-get install phpmyadmin
# select apache 2
# select “keep the local version currently installed”
# again, select “keep the local version currently installed”
# yes to “ Configure database for phpmyadmin with dbconfig-common?”
# input the root password for mysql that you just set
# set your phpmyadmin pass
# Possible your mysql data permissions may need to be fixed

copy contents of “/etc/phpmyadmin/apache.conf” into end of “/etc/apache2/apache2.conf”

/etc/init.d/apache2 restart

#Had to set mysql pass again
/usr/bin/mysqladmin -u phpmyadmin password 'yourpaas'

#good to go
#be sure you can access port 81
http://yoursite.com/phpmyadmin/