"Subphysical" means "pertaining to the realm of reality
that is 'below' (more fundamental than) the apparent
physical universe that we see all around us".
We know that the apparent physical universe that
we see around us is not the most fundamental level of
existence. The technical explanation for how we know this is
beyond the scope of this website but is available in books by
physicists. However, I can summarize it by saying that
quantum mechanics demonstrates the existence of an
essentially infinite number of parallel universes consisting
of every possible arrangement of subatomic particles that
can exist at any distance from the observer. Clearly this is
not what we observe in everyday life, so there is at least
one further level of existence.
Of course there are many other possible consequences
besides those mentioned above, but the most obvious ones at
this early time in the development in this theory are:
Yes, we should expect it to be rule-governed. The reason is
that living creatures can affect their environments in
purposeful ways to achieve goals, which would not be
possible if the subphysical realm were chaotic or random
rather than rule-governed. Human beings are the only known
living creatures who can do this consciously, but all living
creatures do it, or they could not survive.
Physical law is based on quantum mechanics. While there are of course other levels of explanation of the physical realm besides quantum mechanics, that is the most fundamental level of explanation in the physical realm.
Subphysical law must have an analogous "most fundamental" level of explanation, as otherwise we are faced with an infinite regress. Of course we know almost nothing about the subphysical realm, as it has just been discovered. But what we do know is that it is more fundamental than the physical realm. Hence, its law must also be more fundamental than physical law.
Subphysical law is to physical law as a hypervisor is to an
operating system.