I can't hear any sounds from the speaker

I bought an iPhone 4S off of eBay for Xmas for my daughter. I tested it before I wrapped and everything seemed to be working but she figured out problems within 5 mins.

The speaker doesn't work. When you talk to Siri, you can't hear anything. If you press the up and down volume button, the ringer says it is getting louder or quieter but you don't hear any ringing. If you go to settings to change ringtones, you hear nothing. If you plug-in an earpiece, you can hear everything through the ear piece that you should hear via the speaker.

The listing never mentioned these problems but did mention the front screen was replaced and there was "ghosting" when you pressed hard on the screen. I'm not sure if this is important or if it is related.

I have tried to clean the earphone jack with a q-tip. I have also tried cleaning the connector dock with a q-tip very lightly damped with alcohol. I have air-sprayed both parts as well for debris. Still nothing.

Is it possible that the person who replaced the screen did not reconnect something? Any ideas on what parts to order? I'm starting with the battery as the phone won't stay charged for more than 6 hours with the lightest of use. Could this be why the speakers aren't working?