1.remove symlink to phpmyadmin.conf file

rm /etc/apache2/conf.d/phpmyadmin.conf

1. make apache listen on port 81

sudo nano /etc/apache2/ports.conf

  NameVirtualHost *:80
  Listen 80
  Listen 81
 <IfModule mod_ssl.c>
       # SSL name based virtual hosts are not yet supported, therefore no
       # NameVirtualHost statement here
        Listen 443
     </IfModule>

3.Now create the vHost:

        sudo vi /etc/apache2/sites-available/phpmyadmin

              <VirtualHost *:81>
               ServerName phpmyadmin
               DocumentRoot /var/www-81
               </VirtualHost>

4.Enable the vHost

    sudo a2ensite phpmyadmin

5.restart the Apache

     sudo service apache2 restart

1. Create a symlink to the phpmyadmin directoy:
   cd /var/www-81

       sudo ln -s /usr/share/phpmyadmin/
   

phpMyAdmin is a web application, not a daemon. You will have to make your webserver listen on that port and then edit your vhosts so only that port has access to phpMyAdmin.