I found the problem.
I needed the right version of intl. I'm running php 5.3, which I think is the reason that when I ran:
sudo port install php53-intl
it worked.
Significantly, the parent folder also was named the same in the src and destination in the copy.
So my final process was:
sudo port install php53-intl
sudo cp /opt/local/lib/php54/extensions/no-debug-non-zts-20090626/intl.so /usr/lib/php/extensions/no-debug-non-zts-20090626/
sudo pico /private/etc/php.ini
add
extension=intl.so
then
sudo apachectl restart