A prepositional phrase is a group of words that has a preposition as its headword followed by an object (noun, pronoun, gerund, or clause) and any words that modify the object.
Here are the possible patterns of these types of phrase:
Prepositions can be single words such as to, of, about, before, behind, in, with, despite, but also multi-words such as in front of, in spite of, because of, near to, ahead of.
The purpose of a preposition is to draw out the relationship between a noun or pronoun and another word in a sentence.
These are examples of prepositional phrases based on the first pattern as they just contain preposition + noun, pronoun, gerund, or clause but there are no modifiers.
Preposition + noun
Preposition + pronoun
Preposition + gerund
Preposition + clause
Preposition + modifier + noun / pronoun / gerund / clause
Modifiers can then be added to some of these to make the second prepositional phrase pattern:
It functions as an adverbial phrase when it modifies a verb.
If we take a look at some of the same sentences as above for preposition + noun / pronoun, in all of these cases the phrase is modifying the verb that precedes it. It is therefore acting as an adverbial.
Remember that adverbials give additional information about time, place, manner, purpose, condition, result, reason, and concession. They answer questions such as where, when, why, how.
Here are some examples. The prepositional phrase is in red and the verb being modified is in blue:
Prepositional phrases can also act as adjectives by modifying nouns. The noun is in blue and the prepositional phrase modifying it as an adjective is in red:
The phrases are acting as adjectives because they are describing the noun.