Now, just a few words about adverbs and adverbial phrases. adverbsial phrases have the same function as an adverb. There is just the slight difference that it just does not consist of only one word, but of several words. Still, this phrase specifies an adjective, a verb or another adverb.
He left in the early morning hours.
Actually it would be more precise to always talk about adverbials, then both the word (adverb) and the word group (adverbial phrase) would be included.
adverbial = adverb
You can do it later.
adverbial = adjective
He went fast to his car.
She is pretty fast.
adverbial = derived adverb
Luckily he could answer all the questions in the exam.