This study investigates how incorporating phase‑change materials (PCMs) into LHPs enhances passive thermal management by mitigating transient instabilities. This research uniquely assesses system dynamics from both energy‑balance and response‑time viewpoints. The experiments compared a conventional LHP with LHP‑PCM assemblies that employed several paraffin grades. PCM integration substantially increases thermal inertia, prolonging start‑up time and reducing transient temperature rise rates. Cumulative heat‑load analysis confirms that the PCM functions as a time‑based energy buffer, dispersing energy absorption over extended periods and yielding a steadier temperature profile. Steady‑state tests show that PCM use lowers thermal resistance and boosts effective thermal conductivity while maintaining core heat‑transport performance. The nonlinear dynamic analysis further demonstrates that the PCM dampens rapid instability modes and reinforces slower modes by elevating effective heat capacity. The study concludes that PCM act as dynamic regulators, producing a thermal‑management system that is more adaptive, predictive, and resilient to load variations. © 2026 The Author(s).