<p>Thermoelectric (TE) materials are widely investigated for their ability to directly interconvert electrical and thermal energy, with applications in waste-heat recovery, renewable energy and energy storage. As a quantum many-body problem in strongly correlated systems, exploring the elementary excitations and the complex couplings is crucial for designing and optimizing efficient energy-conversion materials. For TE materials, electronic manipulation and thermal transport engineering are two effective strategies for enhancing heat-to-electricity conversion efficiency. The lattice thermal conductivity, <i>κ<sub>lat</sub></i>, is the only independent parameter for optimizing the TE performance and attracts the interest of both theorists and experimentalists. Phonon engineering is essential to effectively manage lattice thermal transport. Recent progress in theoretical models and experimental techniques enables us not only to directly simulate and capture the phonon properties but also to establish clear physical pictures of phonon engineering to understand these advanced functional TE materials. An overview of employing the neutron scattering technique to investigate phonon engineering is introduced.</p>