The man in blue quietly stepped up to the window and paid for his ticket with cash. the adjective phrase in this sentence is
a. in blue.
b. up to the window.
c. for his ticket.
d. with cash.

The answer is letter B.

The adjective phrase in the sentence is, "in blue." In blue directly describes the noun or the subject "man" in the sentence. This is the purpose of adjective phrases, they directly describe a noun or a pronoun in the sentence. Adjective phrases can be seen before or after the noun or pronoun in a sentence. In this case, the adjective phrase is found after the noun. 

The third answer is correct.