The Controlled Phase Gate, also know as CPhase or CZ gate, is a two qubit gate that will apply a phase shift to a target qubit only if the control qubit is in a |1⟩ state.
You can create a CZ gate that acts upon the target if in the |0⟩, but it is more common to use |1⟩.
When applied a CZ gate will multiple the entire target qubit quantum state by the phase of the control qubit.
| 1 0 0 0 |
| 0 1 0 0 |
| 0 0 1 0 |
| 0 0 0 e^(iφ) |
Phi (φ) expressed in radians, represents the phase shift angle to apply to the target qubit.