As we have said, the phases and phase changes are effected by both the temperature and the pressure. We can, therefore make a graph of Pressure v. Temperature that shows the phases of a substance that are found at each point. This is called a Phase Diagram.
A generic form of a phase diagram looks like this:
Each of the three regions of the graph represent one phase.
So, if you choose any temperature and any pressure, you can use a phase daigram to tell you what phase of matter the substance will be.
So what happens when you change those conditions?