The quantum phase distributions and variances of strong coherent and phase-squeezed states mixed with thermal light are calculated. We find that the effect of thermal light on the coherent phase distribution becomes important only when the number of thermal photons is of order one-half. Its effect on the phase distribution of phase-squeezed states (for the case where the number of photons is very large compared to
e2r) becomes important when the number of thermal photons is of order $\frac{1}{2}{e}^{\ensuremath{-}2r}$, where
r is the squeezing parameter.