Our world is, in essence, twofold: there is the material world, which has its own studyable properties, objects, and patterns, but there is also the world of experience within oneself, which can also be examined. In our modern culture, with the proliferation of material sciences, it is easy to brush off the study of the space of human experience.
Phenomenology refers to just that - the study of the space of human experience, as its own scientific universe of objects. At the end of the day, the fundamental question of phenomenology is: what are the objects and the mechanics of human experience, and in what ways does it relate to the material universe?
Categorization in this way serves to divide these landscapes into two: the material and the phenomenological. Dividing them as such is helpful, but here I will demonstrate they are tightly interrelated.
Now, allow me to illustrate the worldview which I wish to demonstrate fraudulent. This is the worldview that sees the material world as ultimate, and assumes that phenomenology is "the result of chemicals in the brain", as though nothing more than shadows cast by the "more real" world of objects dancing above: noticeable, yet inconsequential. In this worldview, chemical and physical events in the brain cause certain emotions to happen. Few would argue against the idea that the happenings of the material world affect what one experiences, but it is not nearly as unanimous a belief that the reverse direction is true: that our experiences themselves affect the physical world.
Someone who holds such a worldview could argue: "A robot can react to the world without any true form of experience. Similarly, the material world acts upon us, and then the physical and chemical happenings within our brains yield both a physical reaction and a corresponding sensation which does not contribute to the physical reaction."
I assert that this view is false, and that the sensation itself contributes to the reaction. Below is my reasoning.
To show that phenomenological experience acts upon the material world just as much as the opposite obviously occurs, I will introduce a way of thinking which works as something of an intellectual crowbar, allowing us to reason about the nature of the phenomenological world. Using it, I will show that phenomena within the psyche affect the material world, and that, in turn, will work as a springboard for more interesting findings.
I understand that the proof will seem lofty and hard to understand, so I will provide an analogous pre-proof first, which is more concrete yet functionally identical. In this pre-proof, we will demonstrate, in roundabout fashion, that human fingers can affect the material world. We notice that the fingers are in an organized array most useful to serve evolutionary function, and thus we can conclude that this property has been selected for evolutionarily. Since they have been selected for evolutionarily, we know that historically some individuals would have had to had fingers in a less optimal layout, perhaps no fingers at all, perhaps fingers shaped less optimally. They must have been selected against historically, and that can only happen if their fingers affect their chance of survival, by affecting the material world. And there you have it, fingers can affect the material world.
Now the real proof. You, the reader, start by observing that your emotions align with that which is evolutionarily beneficial for you. When something happens to you which is evolutionarily negative, you feel a negative emotion. When something damages your body, you feel pain. When you satisfy your evolutionary drives such as eating or reproducing, you experience positive emotions*. It is easy to take this for granted: if we assume the bolded claim to be false, this could easily be switched on its head where you feel positive emotion when in danger and negative emotion when succeeding evolutionarily, even if you'd still behave to achieve sexual pleasure and eat food as much as it may pain you to do so. If we assume the bolded claim to be false, it makes no difference what emotion is mapped onto by which state of the material world. In reality, this is not the case and your emotions are indeed aligned with your physical environment in this way. It is too much of a coincidence (up to the combinatorics of the ways we could re-permute the emotions) to assume that this would be the case if it were not evolutionarily beneficial. This means that, for this feature to have developed evolutionarily, your ancestors must have been selected for or against, based on this property. For selection to occur, the feature being selected for must affect the probability of reproduction of the individual, and thus must affect the material world. And like that, we have our result: your internal experiences affect the material world.
It should be noted that this "proof" has two minor faults which I was able to identify: