The pronoun 'us' is the first person, plural, objective; a word that takes the place of a noun for the speaker and one or more others as the object of a verb or apreposition. The corresponding first person, plural, subjective pronoun is 'we'.Example: John and I ordered the special. We were told that they were out so they made something special for us.
No, a prepositional phrase consists of a preposition and its object (either a noun, pronoun, or gerund) along with any modifiers. The noun in a prepositional phrase acts as the object of the preposition, showing the relationship between the noun and other elements in the sentence.