Optimizing the performance of turbofan engines across various flight phases is a fundamental challenge in aerospace propulsion design, primarily due to its direct impact on operational costs and propulsion stability. This study presents a comparative analysis of the effects of key design parameters, including bypass ratio (BPR) and fan pressure ratio (FPR), on engine performance indicators during two distinct flight regimes: cruise and descent. The primary innovation of this research lies in the simultaneous evaluation of the engine's thermodynamic behavior in these two phases, identifying how the sensitivity of thrust components and efficiency metrics shifts in response to design choices. To this end, a thermodynamic model was developed in MATLAB to simulate parameters such as thrust, thrust-specific fuel consumption (TSFC), and thermal, propulsive, and overall efficiencies. The results indicate that increasing the bypass ratio significantly mitigates the performance disparity between cruise and descent phases. Specifically, the propulsive efficiency gap between these two phases decreases from 8% in a pure turbojet configuration to 4% at a bypass ratio of 8. Furthermore, as the bypass ratio increases, the rate of fuel consumption reduction in the descent phase becomes more pronounced compared to the cruise phase, reaching a difference of 3.15% at a BPR of 8. These findings underscore the critical importance of integrating descent-phase characteristics into the optimization process of high-bypass-ratio engines.