You don't want to "open a port", you want to setup a web server.
By default web server listens at port 80 for HTTP, or the web server opens that port for you. Your site is stored at a folder, you can call it "www", but that is not "AKA" 127.0.0.1, and if you serve it to other computers, you cannot let your web server listen at 127.0.0.1 only. Furthermore, if the access is restricted to LAN only, security may not be a issue, but keep such security concern in your mind when you setup a server for other to access your files. Please make sure you understand such stuff before continuing.
You can start by installing
apache2 package, and your web server is up and running (The files are stored at
I suggest you Google something like "ubuntu apache php" to find tons of guides on this topic, i.e., to install, configure a web server capable of running PHP sites (possibly including a MySQL server), if you encounter some specific problems during this procedure, ask those questions instead.
TIP: it may be more helpful to add your specific Ubuntu version when Googling, like: "ubuntu 14.04 LTS apache php"