The mode of natural selection in which one extreme phenotype is fittest and the environment selects against the others is:
disruptive selection.
uniformitarianism.
stabilizing selection.
artificial selection.
directional selection

Stabilizing selection

Explanation:

Natural selection is a process by which heritable traits conferring survival and reproductive advantage to individuals, or related individuals, tend to be passed on to succeeding generations and become more frequent in a population, whereas other less favourable traits tends to become eliminated.

Disruptive selection, stabilizing selection, artificial selection and directional selection are all types of natural selection. However, unlike others, stabilizing selection tends to lead the population of organisms towards the average trait instead of one or both extremes