electromagnetism - Why there is no phase relationship between the $y$ and $z$ components of electric fields in an unpolarised light

The book says:

if light is travelling along $x$ axis, there is no phase relationship between the $y$ and $z$ components of the electric fields in an unpolarised light, my concern is will there be any phase relation between the two in a polarised light, when the $y$ and $z$ components are just the components of the same wave.

How there will be no phase relationship, I believe it should be 0, if there is no relationship it should be between any two waves not with the components of the same wave.