Phases of matter include solid, liquid, gas, and plasma.
Gibbs phase rule describes the number of phases that can be present at equilibrium for a given system.
In chemistry, phase also designates mutually insoluble substances in contact. One of these layers is typically a hydrophohic layer and the other a hydrophilic layer. For example if you mix water and oil and let it sit, it will separate into two distinct phases. One consists primarily of water and the other consisting of oil.