A novel kind of superimposed fiber Bragg gratings (SI-FBGs) named SI-sampled FBGs (SI-SFBGs) is proposed to control the phase relationship among SI sub-gratings by modulating the sampling periods. The realization of such phase-controlled SI-SFBGs just needs a single uniform phase mask and sub-micrometer precision moving stage. The success of phase-controll is expected to encourage SI-SFBGs' applications in more sophisticated fields. As a demonstration, their applications in spectral-phase en/decoding are testified by both simulation and experiment. The spectral-phase encoded (SPE) encoders with the longest code-length that FBG-based SPE encoders can achieve, i.e., 64-frequency bins, are experimentally fabricated for the first time. The results show the advantages accompanying the SI-SFBGs-based SPE encoders compared with the traditional methods.