Microorganisms use phase variation to increase population diversity to maximize evolutionary success. One such variation is the smooth to rugose phenotype change in Vibrio cholerae. We determined that the variation between smooth and rugose phenotypes can be controlled by a single nucleotide change in a gene (vpvC) predicted to encode a diguanylate cyclase. The vpvC allele found in the rugose genetic background is more active at producing c-di-GMP while that in smooth genetic background is less active. In support of this finding, disruption of vpvC in the rugose genetic variant decreases cellular c-di-GMP levels, diminishes rugose-associated phenotypes and yields a smooth variant. Furthermore, the frequency of phase variation decreases dramatically when the vpvC locus is deleted in the smooth genetic background. Evidence is presented that the rugose variant is less susceptible to phage infection than the smooth variant. As phage infection is known to control populations of V. cholerae and thus outbreaks of cholera, phase variation may increase the evolutionary success of the pathogen.