Here "us" refers to the people of Israel that were living in Egypt. The speaker includes himself as one of the people whether he lived in Egypt or not. (See: [[rc://en/ta/man/translate/figs-inclusive]])
Here "voice" refers to the whole person and his cries or prayers. AT: "he heard our cries" or "he heard our prayers" (See: [[rc://en/ta/man/translate/figs-metonymy]])