portconf is a utility to set per-port Makefile options. Configurations are set in /usr/local/etc/ports.conf.
When using portconf, anytime you run make config and set options manually, they will override any changes made in portconf's configuration. The two configurations will be cumulative, with the settings from make config overriding portconf.
As a result, best practice would be to put all port-specific settings in ports.conf, and not use make config.
Run make rmconfig to reset any settings created by make config. This will allow portconf to use all of it's options.
The port itself provides some sample syntax:
# this is a comment *: NOPORTDOCS editors/openoffice-3: WITH_CCACHE|LOCALIZED_LANG=it print/ghostscript-* print/lpr-wrapper: A4 sysutils/fusefs-kmod*: !KERNCONF | !NOPORTDOCS www/firefox-i18n: WITHOUT_SWITCHER | FIREFOX_I18N=fr it x11/fakeport: CONFIGURE_ARGS=--with-modules="aaa bbb ccc"
Here's an example that could work with a BAMP stack:
databases/rrdtool: WITHOUT_PERL_MODULE graphics/ImageMagick-nox11: WITHOUT_FREETYPE | WITHOUT_FONTCONFIG | WITHOUT_JASPER | WITHOUT_JBIG | WITHOUT_LCMS2 | WITHOUT_LQR | WITHOUT_PDF | WITHOUT_PERL | WITHOUT_TIFF | WITHOUT_WMF | WITHOUT_FFTW | WITHOUT_FPX | WITHOUT_SVG | WITHOUT_WEBP graphics/php53-gd: WITHOUT_TRUETYPE | WITHOUT_T1LIB mail/postfix: WITH_TLS net-mgmt/collectd5: WITHOUT_BIND | WITH_APACHE | WITH_MYSQL | WITHOUT_PING | WITHOUT_SNMP www/apache22-worker-mpm: WITHOUT_DAV | WITHOUT_DAV_FS | WITHOUT_CGI | WITH_SUEXEC