Strange, since the .net DNS server
does resolve it. I just installed AndroIRC on my Note 3 (I haven't been active on IRC in many years, even though I still have mIRC installed on my PC), and it connected to freenode like lightning - really fast.
Try it on your PC with an IRC program (if you have none, try
mIRC: Download mIRC ) and see if you can connect to freenode. If that doesn't resolve, call your internet provider's tech support number. (I suspect that when the phone isn't connecting, the PC won't be either.)
If the port number needed to be changed, you wouldn't get an "unable to resolve" error - all that's "resolved" is irc.freenode.net. The port number is used after name resolution and connection to the server. (And, since 1995, when I first got on IRC, I don't know of any public server that hasn't had port 6667 open.)
If you have further problems, create a free account here, and add a Quick Reply, so we can keep the conversation "in channel", so to speak.