This question is incomplete because there are not underlined sections; here is the complete question:
I helped my younger brother build a sand castle at the beach.
My brother dug a giant hole using only a small pail and shovel.
After we built a sand castle, we jumped into the ocean for a swim.
At high tide, our sand castle was washed away by the waves.
The answer to this question is I helped my younger brother build a sand castle at the beach.
Explanation:
A phrase contains two or more words that are part of an idea or sentence. However, a phrase differs from a clause or a complete sentence because it does not contain a subject and a verb. This occurs only in the sentence "I helped my younger brother build a sand castle at the beach" because the underlined section contains a preposition and its object but not a noun and a verb. Also, this section is part of a complete sentence. Moreover other underlined sections such as "we jumped" o "my brother dug" are not phrases because these include a subject and a verb.
