Heterogeneous multi-core systems are imminent in the multi-core era primarily due to their potential for power-performance efficiency. And programs exhibit phase behavior. To fully tap into the potential of the heterogeneous multi-core systems, the program must be scheduled to the core whose resource availability closely matches its current resource requirements. To solve the scheduling problem on these systems, we propose a Phase Guided Scheduler (PGS) that does the scheduling using requirement factor, a novel measurement combining the program's overall and current requirements. This approach matches the characteristics of the programs and cores without frequent program migration, and guarantees the load balance of cores. The evaluation on Linux 2.6.67 and AMD Opteron 2384 demonstrates its advantage over other heterogeneity-agnostic and heterogeneity-aware schedulers.