Answer:
You need to describe with detail as much as you can, it physical appearance.
Step-by-step explanation:
To assign the phylum of an animal you should compare the size, the kind of body (if it is with a shell, scales, etc.), the size and shape of their eyes, nose, etc. The number of feet (if it has), and maybe you can analyze some of its blood to do a comparative genetic analysis with similar animals. Also, if you find more than one animal, you can compare the inner structure as their digestive system, reproductive system, etc.