Technically, Bluetooth is neither because it is not physically connected to either the phono inputs or the line inputs, thus eliding this whole mechanical quandary altogether. If we are to think of the former as analogous with the necessity for a preamp stage and the latter as being analogous with the lack of this necessity, then I suppose we can think of Bluetooth as line switch, for it is its own amplification and thus would not, were it needed, require preamplification via the phono stage. Any turntable setup, however, would be remiss without at least having the option to use one.