I may have missed it, but have you completely disabled your kids connection to the router while you are running the tests (laptop vs smartphone)? I'm just thinking on the aspect of eliminating all the variables. I'm assuming your smartphone connects to a cell service and not your router? Just probing a little bit....
The kids and my wife all connect wirelessly through various laptops and devices. My home office is the only wired room, with a gigabit switch serving two machines, and then a 40-foot line to the router in another room. To take the switch and line run out of the equation I cabled my laptop directly into the router and had the same results. During these tests the smartphone was connected wirelessly to the router. We only get a very shaky 3G up here and I would never get close to the speeds I'm seeing through the wireless connection. I just re-ran the test on Speakeasy and got 5.5 mbps up/5.5 mbps down wired, and 5.5 mbps up/22 mbps down wireless. So something definitely seems wrong with the wired lan side. I tried different ports as well.
