Recently, Phase-change RAMs (PRAMs) are considered to be as a good candidate that can substitute as DRAM cache buffers (CBs) in NAND flash-based storage devices (NFSDs). PRAM is an adequate device to mobile consumer electronics thanks to low static power consumption, high density and non-volatility. However, in spite of many advantages over DRAM, asymmetric write/read speed of PRAM causes performance degradation in NFSD. In this paper, hence, we first propose a novel scheduling method for an NFSD with PRAM CB utilizing read-while-write (RWW) of PRAM. The method schedules NFSD's requests to service read and write simultaneously using RWW. In the experiment result, the proposed method reduces read and write latency on average by 30% and 19%, respectively.