1. Make your voice louder. Your voice is too soft.

2. Make your voice high.
3. Make your voice up.
4. ______________________
5. Speak up. They can't hear you clearly.
6. Raise your voice in reading the text.
I can't hear you clearly.
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His voice is so soft when he reads the text. In this case, which directions can we use to make him raise his voice? Do you have some more common expressions for that?

1 answer

When referring to one's voice, soft means very quiet. A loud voice, of course, can be heard for a long distance. A high voice means it sounds like a child's or a woman who is singing high notes on the musical scale.

1 is fine.
2 and 3 don't mean the same as 1.
5 and 6 are fine.

His voice is too soft when he reads the text. He needs to read more emphatically.

... more loudly.
... thunderously.
... powerfully.
... emphatically.

Remember that the thesaurus is where you can find words that have similar meanings, but be careful. Not all are one-for-one substitutes!
http://www.thesaurus.com/browse/loud?s=t