Answer:
Noun
Step-by-step explanation:
'Panda' is a noun and 'small' is an adjective. An adjective (small) describes a noun (panda).
An adverbial phrase typically describes why, when, how, or where something takes place or is done. Since there is no verb in the phrase, I don't think it can be an adverbial phrase because there is no verb for an adverb to describe. I think there has to be an adverb in the phrase for it to be an adverbial phrase.
'A small panda' is just talking about the state of the panda, not describing something that panda did or something did to the panda.
Did that help at all? I always feel like what I'm writing sounds smart but to others it sounds like complete and total gibberish. I really hope this helped. I would double-check just to make sure tho
Have an awesome rest of your day!