You could always do it the following way so that all users get access to it. So rather in each individual vhost file, you have one global file. Check my writeup of roundcube on this forum.
Add this to /etc/apache2/apache2.conf
=============
# Include generic snippets of statements
Include /etc/apache2/conf.d/
================
Then add the following file: /etc/apache2/conf.d/phpmyadmin.conf
========================
# phpMyAdmin default Apache configuration
Alias /phpmyadmin /usr/share/phpmyadmin
<Directory /usr/share/phpmyadmin>
Options Indexes FollowSymLinks
DirectoryIndex index.php
# Authorize for setup
<Files setup.php>
# For Apache 1.3 and 2.0
<IfModule mod_auth.c>
AuthType Basic
AuthName "phpMyAdmin Setup"
AuthUserFile /etc/phpmyadmin/htpasswd.setup
</IfModule>
# For Apache 2.2
<IfModule mod_authn_file.c>
AuthType Basic
AuthName "phpMyAdmin Setup"
AuthUserFile /etc/phpmyadmin/htpasswd.setup
</IfModule>
Require valid-user
</Files>
<IfModule mod_php4.c>
AddType application/x-httpd-php .php
php_flag magic_quotes_gpc Off
php_flag track_vars On
php_flag register_globals Off
php_value include_path .
</IfModule>
<IfModule mod_php5.c>
AddType application/x-httpd-php .php
php_flag magic_quotes_gpc Off
php_flag track_vars On
php_flag register_globals Off
php_value include_path .
</IfModule>
</Directory>
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