First, forget the supposed rule that pronouns refer to the most recent noun mentioned. It's not really how they work. As a reader, you should try to figure out the antecedent by looking at what would make the most sense. As a writer, you should only worry if there is a possibility of confusion, which there isn't in this case. If there is a possibility of confusion, you should make the situation unambiguously clear by more means than just the word order.
On the other hand, it is perfectly possible for the antecedent noun phrase to be in a prepositional phrase or a genitive phrase.
Moving on to grammatical issues, it's actually impossible for the antecedent to be "Gilbert’s vibrant description" in this case because that is the subject of the sentence, and "it" is the object. When the subject and the object are the same, we generally need to use a reflexive form, something like this:
Furthermore, Gilbert’s vibrant description of Naples’s pizza makes itself
sound unique and delicious.
Since a reflexive form is not used in the original sentence, we know that the subject and object refer to different things.
"It" can't refer to "Gilbert" because he is a person. The remaining possible antecedents for "it" in the sentence are "Naples" and "pizza." Since cities are usually not described as "delicious," we know that "it" must refer to "pizza."