Prepositional phrases are groups of words beginning with a preposition like "of", "as", or "like" followed by a noun, and they provide more information about a preceding noun. Most prepositional phrases follow verbs to indicate place or time of an action, and phrases using time and place prepositions like "around" or "in" can begin sentences followed by a comma. When checking for prepositional phrases, the preposition must be followed by a noun, not a verb.