Answer:
Phenotypic variation is the variation which appears in the phenotype or morphology of the organism. Natural selection is the mechanism of evolution in which the adapated organism to the environment is selected or highly favoured during the course of evolution.
A phenotype is the results of the genetic change which to be established in a population has to be passed on to the generation.
Since variation in phenotypic traits allows the organism to leave indifferent circumstances therefore phenotypic variation proves essential condition to natural selection.