What's in your /usr/lib is immaterial. MacPorts won't use it. It will use its own libiconv port.
What version of Xcode do you have?
What is the "port" command you ran that caused the error? Was it "sudo port install php5"? Or maybe "sudo port install apache2"? And what port did it say failed to build? Was it php5 or apache2 or maybe instead one of its dependencies?
Whatever port failed, can you please clean it and then try again, this time with the debug switch, and send us all the output? For example if apache2 was the port that failed, then:
sudo port clean apache2
sudo port -d install apache2 2>&1 | tee ~/Desktop/output.txt
Then, assuming that fails again, attach output.txt from your desktop to this ticket.
