What does an organism’s phenotype describe

Phenotype refers to observable traits of an organism physically.

Explanation:

The phenotype is the characteristics or physical expression, of that trait. When 2 individuals that have even the variation in their genes are said to have different genotypes but it not necessary that it will change the phenotype as well.

Thus, the set of observable traits of an organism resulting from the reaction of its genotype with the outside environment is considered as the phenotype of the individual trait.

"do a testcross with a homozygous recessive plant."