By postulating that consciousness is a fundamental feature of the universe, rather than emerging out of simpler elements, integrated information theory is an elaborate version of panpsychism. The hypothesis that all matter is sentient to some degree is terribly appealing for its elegance, simplicity, and logical coherence. Once you assume that consciousness is real and ontologically distinct from its physical substrate, then it is a simple step to conclude that the entire cosmos is suffused with sentience. We are surrounded and immersed in consciousness; it is in the air we breathe, the soil we tread on, the bacteria that colonize our intestines, and the brain that enables us to think.
The Φ of flies, let alone of bacteria or particles, will be for all practical purposes far below the Φ we experience when we are deeply asleep. At best, a vague and undifferentiated feeling of something. So by that measure, a fly would be less conscious than you are in your deep sleep.