The regulations introduced by the European Commission are becoming increasingly stringent regarding both pollutant and greenhouse gas (GHG) emissions, shifting the focus in the transportation sector toward the development of innovative, environmentally friendly internal combustion engines (ICEs). A plausible short-term solution is represented by plug-in hybrid technology. In this context, the PHOENICE project aims to demonstrate the potential of a plug-in hybrid vehicle optimized to reduce both fuel consumption and pollutant emissions. The synergistic use of ultra-lean combustion, innovative in-cylinder charge motion, and an electrified turbocharger enables an increase in peak indicated efficiency of up to 47%. Moreover, to ensure compliance with EU7 emission standards, an advanced after-treatment system is implemented, consisting of an electrically heated three-way catalyst (TWC), a gasoline particulate filter (GPF), and a selective catalytic reduction (SCR) system.