It could be either. This is determined by the word it modifies.
Adverb phrase:
The house was built on the hill. (modifies was built)
Adjective phrase:
The house on the hill is haunted. (modifies house)
It is an adverb phrase, answering when or where.
adjective phrase
adverb
adverb phrase
This is a sentence (or clause), not a phrase. The adjective is dumb, and the adverb is very, modifying dumb. So "very dumb" is the adjective phrase.
It is a prepositional phrase functioning as an adverb. Hint: A word or phrase that answers the question 'Where?' is functioning as an adverb (I think).
If the phrase describes (modifies) a noun or pronoun, it's an adjective phrase. If the phrase describes a verb, adjective, or adverb, it's an adverb phrase.
adverb phrase
Adverb Phrase
an adjective phrase acts like an adjective and modifies the noun or pronoun in the sentence. an adverb phrase acts like an adverb and modifies the verb, adjective, or adverb in the sentence.
It is an adverb phrase (tells where).
adjective phrase
adverb
adverb phrase
adverb phrase
It is an adverb phrase, although in forms such as "The period after a supernova is marked by stellar collapse" it seems to be an adjective phrase.
This is a sentence (or clause), not a phrase. The adjective is dumb, and the adverb is very, modifying dumb. So "very dumb" is the adjective phrase.
Adverb phrase