Hello, my name is Rusty. Which operating system are you using on your computer?
Ok, that's definitely supported. You'll need to choose your audio input device in order to switch it from the headphone input.
Open the Input pane of Sound preferences (choose Apple menu > System Preferences, click Sound, then click Input). Select the USB audio codec and make it your default device. As long as that is selected, you should be able to hear your turntable. Let me know if you still have trouble.
Did it remain selected? Click here. This is going to be the easiest way. Phono to USB doesn't gain audio quality, a record is analog, and so is the RCA output, so they match. That plugs into your microphone input, and you'll be able to hear it..