ProxyBot's own WebUI (Monitor) comes without any protection and could therefore be viewed by any other person as long as the Server and Port are reachable from the Internet.
This guide shows you how to secure the traffic to and from the Webinterface through SSL encryption and also hide it from others by putting Basic HTTP authentication into place.
This guide is based on and made for Ubuntu 16.04 - if you're using other flavours of Linux or any other Operating System you might be able to use parts of it.
You also need a Domain name or sub domain / hostname that points to your server. Make sure to do this before you move on. Your provider probably already offers a subdomain for the server, otherwise it's on you to point one to it.