If you have light traveling from glass to air at normal incidence, e.g., in an optical fiber with the endface open, the Fresnel reflection coefficient would roughly be $R = |(1.5-1)/(1.5+1)|^2 = 0.04$ which translates to $-14\,$dB loss. Also, the reflected light that travels back in the opposite direction would not have any phase shift w.r.t. to the input light beam.
But when you have another optical fiber mated together with the first fiber, the reflection is typically much lower, e.g., $-35$ to $-40\,$dB with FC/PC type connectors. As far as I understand, the physical construction of two fibers mating inside a connector typically involves at least a part of the fibers (or ferrules) being in physical contact. And it is due to the manufacturing precision and polishing etc. that the reflection losses are reduced tremendously. Is that correct?
And here are my main questions:
1) Is the interface that describes the Fresnel reflection correctly now glass-air-glass or glass-glass or something in between?
2) If it is glass-air-glass, does a component of the reflection also come due to the air-glass part? If so, the phase-shift from that part should be $\pi$. In that case, what would be the net phase shift in the back-reflected light?