Normal-mode splitting (NMS) is an evident sign of strong coupling between the cavity field and movable mirror and is a prerequisite for us to observe many quantum behaviors such as optomechanical squeezing and entanglement. The combination of an optical parametric amplifier and coherent feedback can produce a more obvious NMS. However, the impact of coherent phase on the NMS involving above scheme has not been investigated yet. Here, we theoretically analyze how the phase affects the displacement spectrum of the movable mirror and the noise power spectra of the output field. Introducing the phase of the coherent feedback, the quantum Langevin equation of motion is constructed and solved analytically in the Fourier domain, giving the spectrum expressions of movable mirror’s position and output field. With Routh-Hurwit criterion, the conditions of the system stability are obtained and guaranteed in the numerical simulations. The position and linewidth of normal modes are plotted, varying with feedback phase and strength, parametric gain and input laser power. The spectra of movable mirror’s position and output field varying with analytical frequency are also plotted, under different feedback phases. The results show, with other given parameters, the NMS changes with varying phases from - to . Generally, there is no NMS at a phase near - or , and more obvious NMS in a range around zero phase. The mode separation exhibits asymmetric aroundzero phase, and particularly, the largest mode separation occurs in the negative feedback region. The range occurring NMS and corresponding mode separation are both dependent on other parameters such as input laser power, feedback strength, parametric gain, all of which are plotted and compared. This provides us the convenience to optimize the NMS and optomechanical coupling strength by adjusting multiple parameters. These results show a way to realize stronger optomechanical coupling and hence ground state cooling of a macroscopic mechanical oscillator, and have the potential to be applied to the generation of optomechanical quantum states and sensitive detection of a weak force.