what do you think causes different phenotypes in organisms how does the phenotype depend on its genes (genotype)

They difference in phenotypes is dependent on the genes. The more dominant gene will overpower a recessive gene, or if there are two recessive genes together, that will be the phenotype. When things are cross breaded they introduce different genotypes that allow for different looking phenotypes.

Example: Dominant blue flower (Bb)  mixed with recessive yellow flower (bb)

        B            b

b       Bb          bb

b       Bb          bb

There is a 50/50 chance the offspring will be either blue or yellow