Passive object position in 是...的 structure?
In &quot;是谁打来的电话&quot; , the object is '电话'
[电话]是谁打来的 (places the object before the verb emphasize the object, makes it a more important part in the sentence - The phone call is the topic)

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In &quot;是妈妈做的晚饭&quot; , the object is '晚饭'

[晚饭] 是妈妈做的 (place the object before the verb emphasize the object, makes it a more important part in the sentence - The dinner is the topic)

[的] marks 是谁打来[的] as an 'adjectival phrase' that describes the object to follow. In this case, it describes the object 电话 (phone call? What phone call? The phone call that was made by who)
[的] marks 是妈妈做[的] as an 'adjectival phrase' that describes the object to follow. In this case, it describes the object 晚饭 (dinner? What dinner? The dinner that was made by mother)
是 = (it) is/ (it) was