Here's why:
* Adjective phrases modify nouns. They tell us more about the noun they describe.
* "On hide" is a prepositional phrase. It consists of a preposition ("on") and its object ("hide").
* Prepositional phrases can function as adverbs or adjectives, but not always. In this case, "on hide" is more likely to act as an adverb, describing how something is done (e.g., "The animal was sleeping on hide").
To be an adjective phrase, "on hide" would need to modify a noun. For example:
* "The hide on the animal was soft and supple." Here, "on the animal" is an adjective phrase modifying the noun "hide."
Let me know if you have any other phrases you'd like to analyze!