Select the option that expresses the given sentence in passive voice.

They didn’t repair my phone yesterday.

My phone was not repaired yesterday by them.

The correct passive form of the given sentence is My phone was not repaired yesterday by them.

The active voice of the sentence is They didn't repair my phone yesterday. This sentence is in the simple past tense, which is used to describe an action that happened in the past. The passive voice of the sentence is formed by putting the subject of the active sentence after the verb "to be" and the past participle of the main verb. In this case, the subject of the active sentence is "my phone" and the main verb is "repair." The past participle of "repair" is "repaired." So, the passive form of the sentence is My phone was not repaired yesterday by them.

The other options are incorrect because:

• My phone did not get repaired yesterday by them. is also in the simple past tense, but the word "get" is not necessary in the passive voice.
• My phone could not be repaired yesterday by them. is in the past perfect tense, which is used to describe an action that happened in the past before another action happened. There is no other action mentioned in the sentence, so the past perfect tense is not appropriate.
• My phone had not been repaired yesterday by them. is also in the past perfect tense, but it is more grammatically correct than the first option.
• My phone did not repair yesterday by them. is grammatically incorrect. The verb "to repair" needs to be in the past participle form, which is "repaired."