I don’t know what a login link is but the web server listens on all interfaces so you must have your gateway or iptables wrong. Can you ping the box?
It is not secure to expose http to the public Internet. If you need to administer PBX off site change listening port on SSH (secure shell) server to something other than default (/etc/ssh/sshd_conf then restart service). Open up just the SSH port.
Once you login and authenticate to SSH you can use that tunnel to get to any IP address on any interface connected to your server. It’s like a VPN.