Phase fluctuations on the three-element, 11-cm wavelength interferometer at the National Radio Astronomy Observatory (NRAO) were compared with the difference in the atmospheric water vapor content over the respective antennas along a line-of-sight path to a celestial radio source. At times the correlation coefficient for phase and precipitable water was as high as 0.8. At other times when the minute-to-minute correlation was low, there was still a direct relationship between the rms of the phase fluctuation and the rms of the water vapor fluctuation. This study was conducted as part of an experimental program undertaken by NRAO to predict the severity of the phase fluctuation in the very large array (VLA) telescope proposed for construction.