What a corn snakes phylum?

Corn snakes belong to the Phylum Chordata, Sub-Phylum Vertebrata, Class Reptilia, Order Squamata.

If you would like me to go further I would. There is a sub-order of Serpentines, then Family Colubridae, Genus Elaphe, and finally, Species E. Guttata. [the E. for elaphe. it is binomial nomenclature, when giving the species or scientific name of an animal, usually the genus is given along with the species, and sometimes the genus is abbreviated.]