if you remove all the water from an RBC, what's left besides a phospholipid bilayer cell/plasma membrane?)

Salts, proteins and hormones.

Explanation:

Salts, proteins and hormones are the substances that are present in red blood cells.  Plasma of the blood is composed of 90% water, salts, lipids and hormones. It is also rich in proteins such as albumin, immunoglobulins, clotting factors and fibrinogen. These substances are important parts of blood which made the blood to perform its function to transport nutrients in the body so after the removal of water, Salts, proteins and hormones are present in the red blood cell.

answer; polycythemia is the correct answer;