Final answer:
Observation is the best way to identify the external phenotype of an animal.
Step-by-step explanation:
The best way to identify the external phenotype of an animal is through observation. By closely observing the animal's physical characteristics, such as its size, shape, color, and patterns, we can determine its external phenotype. This can be done without the need for complex techniques like electron microscopy, dissection, or DNA analysis. Phenotype refers to the observable traits expressed by an organism, and it can be used to classify and identify different species.