Ok, but what are your typical download speeds using your home wi-fi network? If your home wi-fi is a basic plan with slow speeds, then 1 Mbps download speeds may not be surprising. Or, if you're using the 5 GHz band, remember that download speeds can drop off pretty steeply the farther you get from the router (5 GHz gives you faster throughput but worse range).
Also, I'm guessing that the hotspot your phone is broadcasting is based on the phone's mobile data reception, not your home wifi network, even though the phone is connected to the router via USB.