After the phone gets wet, you do need to give it some time in order to dry out. I don't totally understand it, but basically, once you submerge the phone, the speakers kinda shut off, so the sound you hear is coming from inside the phone, but within half an hour to an hour it'll eventually come back.
Xperia ion - Retired
Galaxy S4 - Backup phone (slightly cracked screen)
Xperia Z2 - Current phone
Xoom 4G - Retired