Review of the linguistic literature on the problems of Phrase Theory in Modern Linguistics

1.4. Prepositional Phrases their contextual features

A prepositional phrase is a group of words including a preposition and a noun, pronoun, or group of words used as a noun. They are fragments that usually do not stand alone, excepr in commands like “At once!” or “On your feet!”.

Kinds of phrases.
There are two kinds of prepositional phrases: adjective phrases and adverb phrases.
An adjective phrase modifies a noun or pronoun. It always comes immediately after the noun or pronoun it modifies:
Joe is the student with the highest grade. (“with the highest grade” modifies student.)
An adverb phrase modifies a verb, adjective, or adverb. It is used to tell when, where, how, or to what extent about the word it modifies:
Megan put her bird in its cage. (“ in its cage” tells where about the verb put.)
Two or More Phrases.
When two or more prepositional phrases follow each other, they may modify the same word, or one phrase may modify the object in the preceding phrase:
They arrived at the airport on time.
(Both phrases modify arrived: “at the airport” tells where and “on time” tells when.)
Chigaeo is on the northeast tip of Illions.
(“on the northeast tip” modifies “is”; “of Illions” modifies “tip”.)
Prepositional Phrase or Infinitive Phrase
Prepositional phrases can be confused with infinitive phrases. “To” followed by “to” followed by a noun or pronoun is a prepositional phrase.

Writing Style Tips.

Some prepositions can also be conjunctions. See conjunction list.
Many prepositions can also be adverbs. To distinguish between adverbs and prepositions, ask yourself whether the word relates a following noun or pronoun to another word in the sentence.¹
Run along. Adverbs = along. + Adverbs do not have an object. Run (along the beach).
(Prepositional phrase ) = (along the beach).
Preposition = along
Object of the preposition = beach.
A preposition has an object and introduces a (prepositional phrase).
This (prepositional phrase) acts as an adverb.
PUNCTUATION
Generally single prepositonal phrases are not separated by commas. A series of prepositional phrases beginning a sentence will be followed commas.
In the summer he swims on the swim team.