I can't hear music, game audio or phone ring unless I have a headphone plugged in but I can hear through the speaker when talking to a person in a phone call. Volume is turned up.
When you say you can hear through the speaker when talking to a person during phone calls, do you perhaps mean that you can hear through the earpiece? Because if so then the speakers on your ZTE Valet may just be busted. If not, then try checking under Settings > Audio profiles to see if any changes there can fix things.