The calculation of phase-space integrals via reverse unitarity and differential equations often faces bottlenecks in fixing boundary conditions. In this talk we present a general and analytical method to derive boundary conditions for phase-space master integrals. Our strategy is based on the auxiliary mass flow method (AMFlow), but it is purely analytic. It is suited for the calculation of boundary conditions near the non-analytic endpoint region of phase space integrals, where a numerical approach is not feasible. We present some applications to DIS-like phase space integrals at two-loops.