Optical magnetic field sensors employ diverse operating principle and sensing media, including magneto-optic crystals, glasses, fibers, and liquids, and range from relatively simple to highly complex and costly systems. In this paper, we report on the development of a fiberized, low-cost polarimetric magnetic field/current sensor based on spectral interrogation. To double the sensitivity, we propose a hybrid configuration combining a fluorescent magneto-optic bismuth silicon oxide (Bi12SiO20) crystal, which exhibits a high, spectrally dependent intrinsic optical activity, with a transparent magneto-optic glass (MOG) exhibiting no optical activity. While a conventional spectrometer tracks three spectral minima, the smartphone-based setup tracks two, which is sufficient for multi-parameter sensing and absolute temperature compensation. Using a 2D smartphone spectrometer, we demonstrate simultaneous spectral interrogation of multiple distinct sensors and demonstrate that this multi-channel topology can be effectively expanded into a 3D vector magnetometer. We also introduce a demodulation protocol that tracks spectral shifts by the separately analyzing the raw red, green and blue (RGB) smartphone pixels, thereby eliminating grayscale-induced distortion. The proposed hybrid BSO-MOG schemes enable the development of affordable, self-compensated current-sensor networks and 3D vector magnetometers using low-cost white LEDs, sheet polarizers, transmission diffraction gratings, and plastic optical fibers.