I think you are misunderstanding what the releases actually are (Lenny/Squeeze etc.)
A Debian build is no more than a kernel, collection of libraries and applications. The applications generally stay the same version, with newer releases becoming available in the next version of Debian (unless someone makes a backport).
For phpmyadmin http://packages.debian.org/lenny/phpmyadmin - You can see that 3.4.10 is available in
This is what makes the OS considered stable - using a (restrictive, not latest) version of software/libs all considered to be stable
You could upgrade to the newer version of Debian, which would be a little extreme for the sake of a small web app like phpmyadmin; or you could just download the latest version of phpmyadmin and install it manually.
When you install phpmyadmin via aptitude, it doesn't do more than create an Apache conf, a system defaults file and populate the contents of
So my suggestion would be to just install
phpmyadmin from the source, it is extremely simple, if in doubt read the README.