  We show that the eight-port interferometer used by Noh, Foug\`{e}res, and
Mandel [Phys. Rev. Lett. {\bf 71}, 2579 (1993)] to measure their operational
phase distribution of light can also be used to measure the canonical phase
distribution of weak optical fields, where canonical phase is defined as the
complement of photon number. A binomial reference state is required for this
purpose, which we show can be obtained to an excellent degree of approximation
from a suitably squeezed state. The proposed method requires only
photodetectors that can distinguish among zero, one and more than one photons
and is not particularly sensitive to photodetector imperfections.
