This is the 14296th most frequent Korean word.
목소리다
"목소리다" is not a correct Korean word. You may mean "목소리," which translates to "voice" in English.
The word '목소리' in this sentence refers to one's actual physical voice or how it sounds.
그의 목소리는 매우 아름답다.
His voice is very beautiful.
Here, '목소리를 내다' metaphorically means expressing one's opinion or making one's voice heard.
회의 중에 자신의 목소리를 내야 한다.
You should speak up during the meeting.
In this case, '목소리를 높이다' means advocating or speaking strongly for a cause.