This study designs and analyses a new phase-coded spread-spectrum communication system where both phase-coded carrier and spreading factor are varied based on a chaotic behaviour in the communication process. This design aims to reduce the probability of interception of the considered system. Discrete values generated by a chaotic map are exploited to create a non-return-to-zero (NRZ)-chaos sequence and simultaneously make bit duration variable. The NRZ-chaos sequence is then modulated by binary phase-shift keying technique to produce the phased-coded carrier. Owing to chip duration being constant, the variation of bit duration also leads to the variation of spreading factor. Spectrum spreading in the transmitter is performed by multiplying directly the variable-duration bits with the phase-coded carrier. A coherent receiver relying on a direct correlator is used for recovering the data. Design of the transmitter and receiver as well as analysis of bit error probability for the proposed system in cases of single-user and multi-user under additive white Gaussian noise channel is presented. Simulation results are shown to confirm the operation of the designed structures and the obtained analytical performance.