**Explanation:**

A system can be defined as a specific portion of the universe that is chosen for analysis. It can be a physical or conceptual entity, and it can be as simple as a single object or as complex as an entire process or phenomenon.

There are different types of systems based on their characteristics. In this case, the question asks about a system comprising a single phase.

**Closed System:**
A closed system is one that does not exchange matter with its surroundings but allows energy transfer in the form of heat or work. It is a fixed mass system. In a closed system, the volume and mass of the system remain constant, but energy can be exchanged.

**Open System:**
An open system is one that allows both energy and matter transfer across its boundaries. In an open system, both mass and energy can be exchanged with the surroundings. This means that the system can interact with its surroundings by receiving or giving off matter, energy, or both.

**Isolated System:**
An isolated system is one that does not exchange either matter or energy with its surroundings. It is a closed system with no transfer of energy. In an isolated system, both mass and energy are conserved, and no exchange occurs.

**Homogeneous System:**
A homogeneous system is one that has uniform properties throughout, such as temperature, pressure, and composition. It is a system in which the constituents are uniformly distributed and cannot be distinguished by naked eye.

**Heterogeneous System:**
A heterogeneous system is one that has non-uniform properties throughout, such as temperature, pressure, and composition. It is a system in which the constituents are not uniformly distributed and can be distinguished by naked eye.

Based on the given information, a system comprising a single phase is called a homogeneous system. This means that the properties of the system, such as temperature, pressure, and composition, are uniform throughout the system.