。
She pretended not to hear his voice.
Literal
She [topic-は] his [genitive-の] voice [subject-が] not-audible pretense [object-を] did.
ふりをする ('to pretend') is a key set construction — attaches to a clause's plain form (聞こえないふりをする, 'pretend not to hear'). The clause inside ふり describes the pretense. Note 聞こえる ('be audible') takes its 'audible thing' with が, not を — it's the intransitive partner of 聞く ('listen'), focusing on whether sound reaches the listener rather than active listening. So 彼の声が聞こえない = 'his voice is not audible (to her)' — she's pretending the sound didn't reach her.