I am making a Unity game. I want to be able to allow the phone to be used as a steering wheel, as input into the PC game.
Technically, How can I achieve this? Can this be done through bluetooth?
You just need to create a server on the computer and a client on the phone. Although this can be done through Bluetooth, in my opinion it's better to use a local connection, since most households have WiFi, but not every computer has a Bluetooth adapter (e.g. desktop computers).
After this it's just basic client-server communication and sensor reading, look up a tutorial in the language you are using.