speak up

1.  Also, speak out. Talk loudly, so as to be heard, as in Speak up, child, I can't hear you, or He should speak out so that those in back can hear him. The first term dates from the early 1700s, the variant from the early 1500s.
2.  Also, speak up for. Express one's opinion or one's support for someone or something. For example, When it comes to speaking up about the town's needs, you can rely on Mary, or I'm glad you spoke up for me in that meeting. [c. 1700]

The verb has 2 meanings:

Meaning #1: speak one's opinion without fear or hesitation
  Synonyms: opine, animadvert, sound off

Meaning #2: speak louder; raise one's voice