First, try the iPhone with another dock or docking iPod speaker to make sure your iPhone is ok. Try one of those iPod speaker systems at the Apple Store, Target, Walmart, Best Buy, etc.
Sometimes, the pins on the LOD flatten out, resulting in poor contact with the iPod. You may be able to pry it up.
Take a look at the pins on the LOD. Looking at the LOD from the point of view of the iPhone, you will see 4 pins on the Right (numbered from Right to Left - Pins 1,2,3 & 4) and Pin 11 nearer the midline.
Pin 3 is the Right channel and Pin 4 is the Left channel. Check to see if Pin 3 is okay. You can also check for continuity with a multimeter. On the 3.5 mm miniplug, the tip should map to Pin 4, the Ring to Pin 3.
Otherwise, I'm sure Hans at Qables would be more than happy to check it out.