I'm new to Ubuntu server, which I have install (10.04). My server is connected to my Belkin router, which in turn is connected to my CISCO Linksys SPA2102 VOIP phone adapter/router. I can asscess my webpages on my server (Apache2 installed) thru my home network. But, I can not access the webpages from the internet outside of my home. I need simple step by step instructions to help me. I have install most required software (openSSH, php5, MySql, and WinSCP).
This is a basic suggestion but you need to forward 80th port to your server: http://portforward.com/english/routers/port_forwarding/Linksys/SPA-2102/Cisco_WVC210.htm
This is not really related to Ubuntu, but to your network. You may have heard that the internet is running out of IP-addresses. This is true for IPv4, which almost all internet service providers use. In order to pretend that there is no problem, they've come up with a technique called Network Address Translation, or NAT for short. What this does, is that it presents you with one public IP-address and then gives you a set of private IP-addresses in your network.
An IP address has a set of ports that are used for services. For instance, web servers use port 80 by default. Since that port belongs to the IP, and the IP belongs to your router, you'll have to configure the router to forward all incoming connections on that port to another IP in your network. This also means that you can't have two web servers using the default port in your network.
I don't know any specifics about those routers of yours, but it is likely that both of them use NAT. In that case, you'll have to forward ports in the first router to the second router, and from the second router to the IP of the computer you wish to use as a server.
This is far beyond the scope of this site. If you can connect and use the services from within your network, then your Ubuntu is fine.