Actually, I think if you look at the phpMyadmin homepage:
You'll see fairly quickly why
But you can (If I'm not mistaken) setup Apache to deal with php3 files instead of installing the .php version.
Look for something like this in your httpd.conf file:
DirectoryIndex index.html index.php index.php3
And add the php3 like I have above.
However, the easiest way to do this correctly is to use the correct package for your version of PHP: