  The $\rho(T)$ curve is traditionally employed to discern metallic,
semiconductor, and insulating behaviors in materials, with any deviations often
interpreted as indicative of phase transitions. However, does this
interpretation hold under the influence of a magnetic field? Our research
addresses this critical question by reevaluating the $\rho(T)$ curve in the
presence of magnetic field. We uncover that metal-insulator shifts and
reentrant metallic states may not indicate true phase transitions but rather
originate from the scaling behavior of magnetoresistance, influenced by
magnetic field and temperature through a power-law dependence. Employing
advanced first-principles calculations and the Boltzmann method, we analyzed
the magnetoresistance of SiP$_2$ and NbP across a range of conditions,
successfully explaining not only the reentrant behavior observed in experiments
but also resolving the discrepancies in magnetoresistance behavior reported by
different research groups. These findings challenge the conventional use of the
$\rho(T)$ curve as a straightforward indicator of phase transitions under
magnetic conditions, highlighting the essential need to exclude typical
magnetoresistance effects due to the Lorentz force before confirming such
transitions. This novel insight reshapes our understanding of complex material
properties in magnetic fields and sets a new precedent for the interpretation
of transport phenomena in condensed matter physics.
