When people colloquially say "speed of light" it understood to mean the speed of light in a vacuum. Light travels slower the higher the refractive index of the medium its travelling through. Saying "nearly the speed of light" indicates that the light is travelling through a medium with a refractive index very close to 1.
To say that light travels at “nearly the speed of light” in any medium is a bad choice of words. Also with refraction coefficient of 1.40 - 1.45 in fiber, the term “nearly” is not appropriate if the intention was to compare with vacuum.
Fiber optic cabling won't transmit at the speed of light due to the refractive index of the medium. So it's slower than the speed of light in a vacuum or atmosphere.
This is funny. Why “nearly”?