It should be noted that in the pair "купи́ть (perf.) - покупа́ть (imperf.)" the imperfective verb has a prefix and not vice versa.
MOSFET, can you give an example within the context of this sentence, using the imperfect form?
Вчера мой брат покупал новый телефон. (the process of buying, not the result). Will be translated with the continuous tense.
is "new telephone" in the accusative case?
Can you say "вчера брат купил новый телефон"?
Yes, "my" is redundant in most cases, especially in speech.
It's still not accepted 2020-12-04