Adjective phrase modifiers in English grammar are words and phrases that that modify or describe an adjective or adjective phrase.
Adjective phrase modifier is a grammatical function.
The grammatical form that can function as the adjective phrase modifier in English grammar is the adverb phrase.
Adjective phrase modifiers are constituents of the adjective phrase.
Brinton, Laurel J. & Donna M. Brinton. 2010. The linguistic structure of Modern English, 2nd edn. Amsterdam: John Benjamins Publishing Company.
Hopper, Paul J. 1999. A short course in grammar. New York: W. W. Norton & Company.
Huddleston, Rodney. 1984. Introduction to the grammar of English. Cambridge: Cambridge University Press.