We explore the exceptional point(EP)induced phase transition and amplitude/phase modulation in thermal diffusion systems.We start from the asymmetric coupling double-channel model,where the temperature field is unbalanced in the amplitude and locked in the symmetric phase.By extending into the one-dimensional tight-binding non-Hermitian lattice,we study the convection-driven phase locking and the asymmetric-coupling-induced diffusive skin effect with the high-order EPs in static systems.Combining convection and asymmetric couplings,we further show the phase-locking diffusive skin effect.Our work reveals the mechanism of controlling both the amplitude and phase of temperature fields in thermal coupling systems and has potential applications in non-Hermitian topology in thermal diffusion.