In music, a phrase is typically the longest among the options given. A phrase can be thought of as a complete musical thought, much like a sentence in language, and it usually consists of several measures.
- A motive is a short musical idea.
- A cadence is a harmonic punctuation marking the end of a phrase or section.
- A climax refers to the peak or most intense part of the music, but it is not specifically defined by length.
Thus, the correct answer is phrase.