If I want to say HCl (g), do I need to say the gas form of hydrogen chloride or hydrochloric acid?

The gas form of hydrogen chloride.

Explanation:

Pure hydrogen chloride is a gas. it is formed when hydrogen gas combines with chlorine gas. Tat is indicated by using HCl (g), as you have correctly done in your question. So, strictly speaking HCl is the gas form of hydrogen chloride, and you should not say the gas form of hydrochloric acid.

Hydrogen chloride (the gas) may be dissolved in water, and then it forms aqueous hydrogen chloride, which is indicated as HCl (aq). The solution of hydrogen chloride may also be named hydrochloric acid. So, the name hydrochloric acid should only be used for the aqueous solutions of the acid.