>>24548748 (OP) Phantasms are tied to the material conditions and specific individuality of the sensed object. They are not universal concepts.
According to Aquinas's empiricism, "nothing is in the intellect which was not first in the senses." Therefore, all intellectual knowledge ultimately originates from sensory experience, which is organized and presented by phantasms.
Unlike the phantasm, which is material, the agent intellect is an immaterial power of the soul. It's an active principle, not a passive receiver.
The agent intellect "lights up" the phantasm, making what is potentially intelligible (the universal form within the individual phantasm) actually intelligible. It then performs the act of abstraction, which means separating the universal essence or nature of the thing from its individual, material conditions.