Strong electromagnetic (EM) response at low thickness is urgently required to address the emerging EM radiation pollution. Among numerous methods to achieve electromagnetic response at low thickness, interface construction exhibits some advantages for the combination of numerous dissipation mechanisms. Here, ternary Mo-Ni₂P/rGO absorbers with multiple interfaces are designed via the phosphating treatment at a certain temperature. The constructed heterojunctions can efficiently exploit the high-conjunction of Ni₂P and rGO and the interactions between different dielectric media (metal/semiconductor/conductor) for excellent electrical conductivity, abundant interfacial polarizations, and rational combination of different loss materials. As the phosphating temperature increases from 600 to 800 °C, the Mo-Ni₂P/rGO-800 sample exhibits excellent microwave absorption performance, where the reflection loss (RL) value is −35.43 dB, and the effective bandwidth reaches 3.48 GHz at only 1.20 mm. This study proposes a simple method to enhance the microwave absorption performance at low thickness based on the construction of heterojunction structures. Moreover, an insight into the role of integrating different loss mechanisms in achieving high-efficiency EM wave absorbers has been fulfilled.