Yep, you're right, we can only talk about the phase of matter if we have a collection of molecules. It wouldn't make any sense to talk about a single molecule as being a solid, liquid, or gas because what matters is how the kinetic energy of the molecules (related to temperature) compares to the intermolecular bonding energy.
Solid: KE << BE
Liquid: KE < BE
Gas: KE >> BE
I think the context that this sentence appeared in adds further clarity, so I've included it below.
Here's the full paragraph along with Fig. 3:
The key distinction between the three classes of molecules is
summarized in the bottom portion of Fig. 3. Small molecules may appear
as solid, liquid, and gaseous phases without decomposition, while
rigid macromolecules keep their bonding to nearest neighbors (their
molecular integrity) only in the solid state. Due to internal
rotation, flexible macromolecules can attain sufficient intramolecular
disorder to melt (or dissolve) without breaking strong bonds. This
property is at the root of many of the useful properties of polymers
(plastic and rubber–elastic behavior in addition to high strength,
light weight, and low melting temperatures). The three classes of
molecules are thus very distinct in their phase behavior. No
macromolecule can be evaporated thermally without decomposition. If
one tries to place flexible macromolecules into the gas phase by
evaporation of small solvent molecules from a dispersion of droplets
of a solution with only one macromolecule per droplet, the
macromolecules become microphase particles and collect at the bottom
of the container .