In outlook, tools, options, mail setup, (email)accounts;
Double-click the connection name, possibly your username, most likely Microsoft Exchange. The next dialog will have the address under microsoft exchange server. Write that down, get a command line (start run cmd) and type
Ping that.address.from.above and write down the IP address (192.168.2.3 or whatever). Use that address in setting up your phone, the reason being is that sometimes networks have internal or 'short' names that your phone will not know about if you are on 3g or Edge outside of the regular network (aka wifi). the ip address as the server name pretty much means that you can find it from any network.