Was just looking at Audacity, it does not seem to offer ASIO support. This may be the issue.
1. The FireStudio Mobile (FSM) has mic/line level inputs. But no phono inputs. If the turntable has line level outputs, then connect those to the FSM, create a stereo audio track in Audacity, set levels and record.
2. If the turntable only has phono outputs, the tables would have to be connected to a turntable mixer that has phono ins and line level outputs.
Should the conditions of number 1 be met, and you still are not getting a level on record, please create a support ticket. After checking, I can see you also have a copy of Studio One 3 Artist in your My.Presonus.com account that you can use to set this up with.