Final answer:
The adverbial phrase in the sentence 'Jennifer scrubbed the bathtub until her arms ached' is 'until her arms ached', as it provides further detail about the duration of the action.
Step-by-step explanation:
In the given sentence, 'until her arms ached' is the adverbial phrase. Adverbial phrases function like adverbs, providing additional information about when, where, why, or how the action occurred. In this context, 'until her arms ached' tells us more about the duration of Jennifer's scrubbing the bathtub, thus modifying the verb 'scrubbed'.
Learn more about Adverbial Phrase