[Rasta]

Mach das einfach in deine config

server{
...
    location /phpmyadmin{
        root    /usr/share;
        index   index.php;
    }

    location ~ \.php$ {
        set $php_root   $document_root;
            if ($request_uri ~* /phpmyadmin) {
                set $php_root /usr/share;
           }

        fastcgi_pass   unix:/tmp/fastcgi.socket;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME  $php_root$fastcgi_script_name;
        include /etc/nginx/fastcgi_params;
    }
}