Losing one's voice

лишиться [no Impf.] голосаg;
терять/потерять голосa
to lose one's voice
NB With терять голос the adverb постепенно "gradually" can be used, but with лишиться голоса it cannot.
пропадать/пропасть: у Ng голосn пропал N lost his voice
После болезни у него пропал голос. He lost his voice after his illness.
садиться/сесть: у Ng голосn сел N's voice has become hoarse and weak
NB The phrase у N голос сел, above, describes a voice hoarse from exertion, overuse, a cold, etc.
Пришлось отменить концерт: у певца сел голос. The concert had to be postponed: the singer had lost his voice.
срывать/сорвать голосa to strain one's voice