The word "suddenly" is already an adverb, meaning it describes a verb, adjective, or another adverb. It is not a phrase.
Adverb phrases are groups of words that function as adverbs. They usually include an adverb and other words that modify it.
Here are some examples of adverb phrases:
-
very quickly
-
all of a sudden
-
in a hurry
-
with great care
These phrases describe how, when, where, or to what extent an action is performed.
While "suddenly" can be part of an adverb phrase, such as "all of a sudden," it is not an adverb phrase itself.
