The growing demand for efficient and sustainable last-mile delivery has led to the rise of advanced delivery systems, where autonomous delivery robots work alongside vans to enhance logistics efficiency. However, existing models follow rigid routing structures, which makes it difficult to handle parcels split into multiple modules. This paper introduces the Two-Echelon Vehicle Routing Problem (2E-VRP), a novel approach that considers modular parcel logistics within the Physical Internet (PI) paradigm to create a fully connected, traceable, and reconfigurable delivery system. The proposed model ensures that the components of a parcel are consolidated at the final destination while dynamically optimizing transshipment between vans and robots at the robots' drop-off points. By leveraging the enhanced connectivity and real-time data sharing offered by the PI framework, the model optimizes robot capacity utilization and significantly reduces sidewalk congestion. The system minimizes the number of active vehicles, delivery times, energy consumption, and the gap between the first and last module deliveries, thereby improving overall delivery precision. Furthermore, computational experiments comparing the cost functions of the modular and unique parcel formulations have been analyzed and discussed.