Question

the smallest biological unit that can evolve is the species individual phylum population

Explanation:

Evolution occurs through changes in allele frequencies over time. An individual's genes do not change during its lifetime to cause evolution. A species is a larger group, and a phylum is even broader. A population (a group of individuals of the same species in a given area) is the smallest unit where allele frequency changes (evolution) can be observed as a result of processes like natural selection, mutation, etc.

Answer:

population