Partial Transmit Sequence (PTS) is an efficient distortionless technique to reduce the high peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM). A class of continuous-phase PTS (CP-PTS) schemes has been proposed for improving the PAPR reduction performance. However, the phase factor values of CP-PTS are in a continuous domain so that the desired side information (SI) is large, which seriously degrades the spectrum efficiency. In this paper, on the one hand, a SI design method is proposed to quantify CP values. On the other hand, a signal detection method is proposed to combat the performance degradation. We show that the proposed methods can make a good tradeoff between spectrum efficiency and system performance.