Adverb phrases modify an adjective or another adverb when they provide more information about the adjective or adverb.
Commonly modifying the degree, intensity, or manner of the adjective/adverb.
They can often be a single word (e.g., quite unsure, extremely unhelpful) but may extend to more than one (e.g., a little disappointed, not entirely sure).
Adverbs can be observed commonly ending with -ly.
They cannot exist on their own (independently) due to being dependent (non-clausal) phrases.
Tag
rb+jjrbmod is tagged on the adverb of the modifying adjective/adverb phrase.
Examples
That cat was surprisingly fat.
We will see those impacts fairly quickly.
Despite the captain’s best efforts, the team was not entirely sure about the plan.
The boy was fairly certain that it would rain due to the heavy smell in the air.
Discussions
We did not tag the prepositional phrase functioning as adverbial phrases.