Final answer:
The group of words in bold is a phrase because they do not contain both a subject and a verb and therefore cannot stand alone as complete sentences.
Step-by-step explanation:
The group of words in bold from the provided sentence is a phrase. A phrase is a group of words that functions as a single unit within a sentence, and it is missing either a subject or a verb.
In the example given, "Just do it" or "When you care enough to send the very best," none of these groupings contain both a subject and a verb, hence these are phrases and not clauses.
Phrases can vary in type and include noun phrases, verb phrases, adverbial phrases, and more, but they do not express a complete thought that could stand alone as a sentence.
The group of words in bold, "Just do it" or "When you care enough to send the very best," is a phrase. A phrase is defined as any word or group of words that functions as a unit within a sentence, but is missing either a subject or a verb.
In this case, the phrase consists of the advertising slogans themselves, and they do not contain a subject or a verb.