This is a phrase that has long been current in many esoteric and mystical circles as a description of the spiritual project. I've used it myself in the past because one normally expresses oneself in the language of the day but also because, let's be honest, I probably wasn't thinking too deeply about what it actually implies.
So, what does it imply? To begin with, is expansion of consciousness necessarily a spiritual thing? One assumes so based on an evolutionary description of human unfoldment, and there is certainly the strong probability that the universe is, in one sense, a machine for the growth of consciousness. In that sense then it is spiritual. Human beings can grow out of their limited earthbound type of consciousness into higher states. But they can do this through drugs and there is nothing spiritual about drugs or the states they bestow. Drugs can give the impression of love, bliss, oneness and all that, as can some forms of mental illness, but this is not spiritual because it relates to effects not inner transformation. Meditation and other spiritual, so-called, techniques can also bring about heightened states of consciousness but the subject is not fundamentally changed by that. He may think he is and he may act in a particular way but deep inside he is not really changed at all for one may have many expansions of consciousness and still remain the same fallen, unredeemed human ego at core. This is true even if the expansionary experiences are, so to speak, not just extending the circumference of the circle but going from a circle to a sphere. In these cases the subject may act as though ego has been transcended but he is the same person, responding to his experience by imitating what he thinks is the type of being that would be stabilised in this experience. And note that these expansions of consciousness are all just temporary anyway.
That is why all proper spiritual teachers tell meditators not to imagine they can do without prayer. The old dream of fallen human nature is to think it can reach godhood without God. This is a wicked lie designed to appeal to the spiritually avaricious ego. It's what tempted Eve to bite the apple and it's what tempts many would-be mystics and esotericists today. Spirituality without God is not possible. That is the major drawback of Buddhism though God is often smuggled in through the back door in that religion.
On a simple linguistic level we can say that something that expands still has the same centre, and from the spiritual perspective it is the transformation of the centre that matters so the very concept of expanding consciousness is not spiritual. This doesn't mean that souls in heaven do not have a transfigured state of being but that is because they have taken on the mind of Christ and no spiritual practice can enable that. It depends of the soul giving itself to God through Christ and then becoming the recipient of grace. It may be argued that this is just a different way of expressing the same thing, expanding consciousness and taking on the mind of Christ is six of one and half a dozen of the other, but the way you express yourself matters because it both reflects and forms the way you think. If you think of the spiritual journey in terms of expanding consciousness you are thinking of it in terms of what the ego can gain and how it can grow. To reach a truly transfigured consciousness is only possible through taking on the mind of Christ and that can only happen through the soul loving Christ and asking nothing for itself other than to be allowed to do so. Everything else is just to make the soul grow by applying growth stimulus from without. This alone grows the soul from within which is the only true way.