The PHENIX detector at RHIC has been designed to study central Au + Au collisions at 200 GeV per nucleon pair. PHENIX measures muons in two muon spectrometers located forward and backward of midrapidity, and measures hadrons, electrons and photons in two central spectrometer arms, each of which covers 90 degrees in azimuth and /spl plusmn/0.35 units of rapidity. The final component of each central arm spectrometer is an electromagnetic calorimeter, which precisely measures the energy and time of arrival of particles created in relativistic heavy ion collisions. The calorimeter also provides electron and hadron identification capabilities by energy-momentum matching with the tracking measurement. It is also used for triggering on high energy photons and electrons. The operation, monitoring, calibration and the analysis methods used to deal with the high multiplicity environment are described. Results on neutral pion and direct photon production will be presented.