Are phosphomonoesterases solid?
Enzymes are very, very large in comparison to the typical molecules you encounter in chemistry (excluding any polymers). A 10 kD protein is considered to be small, and there are proteins of several hundred kD. 

If you remove all the water from a typical protein you end up with a solid. But for most enzymes this would be an irreversible step, and they would lose their activity.

Usually enzymes are kept in aqueous solution, often with some glycerol or other cryoprotectants, and frozen.

Strictly speaking, they would probably be solid, but likely inactive in that form so I'm not sure if it counts. The relevant form of an enzyme is dissolved in water.