1 do u see on the left hand side of ur phone there a little button above volume if it shows red u mute everything.
2 I would get that phone volume checked. I had that happen once on another iPhone 4 and apple tweaked something inside and fixed it. I only could use speaker phone for calls. Apple took 10 min to fix it and they said it could happen again. If ur near an apple store it will be quick to fix.
So u know the speaker on the bottum is for speaker phone ringtones games etc. if u block it ts so quiet. The front for calls they told me isent really a speaker.