Question

how can you know the phase

Answer 1

phase [fayz]
noun (plural phas·es)
1. stage of development: a clearly distinguishable period or stage in a process, in the development of something, or in a sequence of events
2. pattern of behavior: a period of time when a situation or particular pattern of behavior persists and is often annoying or worrying
3. part or aspect: one of the many parts or aspects of something
We needed to restructure all phases of our business.

4. astronomy recurring shape of moon: a recurring form of the Moon or a planet seen in the sky.
The four principal phases of the Moon are the first quarter, full moon, last quarter, and new moon.
5. physics part of repeating cycle: a part of a repeated uniform pattern of occurrence of a phenomenon or process, relative to a fixed starting point or time
6. physics state of matter: a state in which matter can exist, depending on temperature and pressure, e.g. the solid, liquid, gaseous, and plasmatic states
7. zoology variation in animal form: an alternate stage, appearance, or coloring that distinguishes a group of animals from most of their kind, or that an animal adopts under specific conditions
8. biology stage in life cycle: a stage in the life cycle of an organism

Answer 2

Assuming I'm reading into this correctly, you can consult what's known as a phase diagram. Armed with the temperature and pressure of a material, you can use the chart to find which phase it currently holds. http://en.wikipedia.org/wiki/Phase_diagram