Answer: Phenotype
Step-by-step 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 tend to become ELIMINATED
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The factors contributing to natural selection are four. They are reproduction, variation, Heredity, survival fitness level (based on traits).
However, the phenotype (observable characteristic of an organism) DO NOT contribute to natural selection. A plant specie is not selected by nature JUST because it is TALLER, it must also be that that trait of tallness aids its survival or else, it will be ELIMINATED.
So, the all but one factor is Phenotype.