Apache needs to have PHP support, not vice versa. i doubt if Apache that you install from ports has PHP support built in. if it doesn't you need to compile it.
download latest PHP and Apache sources, unpack and follow instructions from INSTALL file in PHP directory. it tells you how to configure it for Apache.
basically you first have to run
./configure
in Apache dir, then switch to PHP dir and do something like (depending on your needs)
./configure --with-apache=/usr/local/apache_1.3.x --with-other-options-you-need
make
make install
(where x is your version number) then switch back to Apache and do once more
./configure --activate-module=src/modules/php4/libphp4.a
make
make install
then copy php.ini-dist from PHP dir to /usr/local/lib (or wherever apache can find it) and you're set.
but do read INSTALL, its has far more presice guidelines.