I'm sorry if the question is too philosophical or makes no sense, but I need to be able to explain why it doesn't make sense. When we take the in-phase and quadrature-phase base-band components of an intermediate frequency signal, it's very easy to show that any one of the two orthogonal components alone would be insufficient to distinguish the variations in a single-carrier phase from variations in its amplitude. This tutorial makes it quite clear. The Q component, although real, carries the imaginary component of the phasor $A(t)\exp(2\pi f_I\cdot t + \phi(t) )$.
However, when we pass the RF signal through a mixer, there is no Q component lost. No phase modulation will be lost in the base-band signal obtained later. Why not? A figure to help create context.