If I'm connected to my home WiFi, using its internet and then us my iPhone 4s Person hotspot on a desktop....would the desktop be using the house internet or my phone's?

If Im Conected to my home WiFi on my iPhone 4s & turn on my phones personal hotspot & connect it to my desktop, Is the desktop using the houses internet or my phones internet???
I want my desktop in my room for me only but I dont have a phonejack in my room & dont wanna add one & I dont wanna long ethernet wire running from the living room to my room in the back of the house.
Please help