expression, godan verb (-ru)
Describes a voice breaking or cracking, often due to emotion, nervousness, or puberty. The verb 裏返る literally means 'to turn inside out', so the image is of the voice flipping or becoming unsteady.
See also: 裏返る (うらがえる)
緊張して声が裏返ってしまった。
I was so nervous my voice cracked.
彼は怒ると声が裏返る。
His voice cracks when he gets angry.