I'll try to answer this question with as few words as I can. FULL BLAST!!! Having your sound unit on full blast is the extreme limit of loudness. About if it's correct to turn the phone off silent, it all depends on where you are. Note: Ian is correct. Mute means to be in silence and to unmute it means to receive sound again. But the opposite of silent mode is FULL BLAST!!!

in USA, we sometimes say "mute". "mute" your phone, "unmute" your phone. that's probably how I would say it, it depends on the situation and the sentence, though.