An Adverb Phrase (sometimes known as an Adverbial Phrase) is – as you might guess – simply a group of words which act in exactly the same way (grammatically speaking) as a single adverb.
For example, here’s a sentence with a single adverb:
The police arrived quickly.
We can expand on that adverb and turn it into an adverb phrase
The police arrived very quickly indeed.
The police arrived really very quickly indeed.
And that’s it. An adverb phrase is simply an adverb with some other words attached to it to modify it in some way.
Types of Adverb Phrases
The simplest type of adverb phrase consists of an adverb with another adverb. Any extra adverb is called an intensifier.
{intensifier} + {adverb}
The dog eats his dinner very slowly.
Oddly enough, your idea worked!
Adverb phrases can be made with prepositions and act as adverbs of manner, place, time, frequency, purpose, etc.
manner
The fireman opened the door with a kick.
place
The house they are building next door is already for sale.
time
I’ll see you all again after the summer.
frequency
Given your past medical history, you should have a check up every year.
purpose
This report is for your eyes only.
Useful Links
Adverbs in English Grammar – a general look at adverbs
Phrases in English Grammar – a general look at phrases