Final answer:
The group of words 'using telescopes that he created' is a phrase because it does not contain both a subject and a verb, which are required for it to be considered a clause.
Step-by-step explanation:
The group of words in bold, 'using telescopes that he created', is a phrase. A phrase is a group of words that acts as a single part of speech and does not contain both a subject and a verb. In contrast, a clause contains both a subject and a verb, and it can express a complete thought if it is an independent clause or an incomplete thought if it is a dependent clause.
The group of words in question lacks a subject performing the action—it only describes the action of using telescopes, which Galileo did. Hence, it cannot be a clause. Therefore, the answer to whether the group of words in bold is a phrase or a clause is Option 1: Phrase.