Learn Hardcore Russian: Мой друг купил телефон на распродаже.

It is a prepositional phrase that indicates the context or setting of the purchase. In this case, it means on sale, showing that the phone was bought during a sale event. The preposition на requires the prepositional case, which is why распродаже appears in that form.

Why is the verb купил used here, and what does its form tell us about the action?

Купил is the masculine singular past tense form of the perfective verb купить, which indicates that the action of buying is complete. The perfective aspect is used to denote that the event (buying the phone) has been finished, rather than something ongoing or habitual.

How does the possessive pronoun Мой agree with the noun друг in this sentence?

In Russian, adjectives and possessive pronouns must agree with the nouns they modify in gender, number, and case. Since друг (friend) is masculine singular in the nominative case, Мой is correctly used in its masculine singular form to match.

What function does телефон serve in the sentence, and why doesn't it have an article like in English?

Телефон is the direct object of the sentence—it’s the item that was bought. Russian does not use articles (such as a or the), so nouns appear without them. The function of the noun is understood through its position in the sentence and its case endings.