Linear phosphate-polyether copolymers (LPC) were synthesized by polycondensation reaction of methylphosphorodichloridate with poly(ethylene glycol) (PEG) and/or poly(tetramethylene glycol) (PTMG) to increase local segmental motion for improved ion transport and ionic conductivity at ambient temperatures. Ionic conductivity and thermal behavior of LPC-salt systems were investigated at various copolymer compositions, salt concentrations and temperatures. The PEG(70)/PTMG(30)/LiCF$_3$SO$_3$ electrolyte exhibited ionic conductivity of 8.04$ imes$10$^{-5}$ S/cm at 25 $^{circ}C$. Salt concentration exhibiting highest ionic conductivity was considerably dependent on EO/TMO compositions in LPC-salt systems. Effect of chain flexibility and solvating ability of host polymer on the ionic conductivity was investigated theoretically with the Adam-Gibbs configurational entropy model. For LPC6 series-salt systems, the temperature dependence on the ionic conductivity fitted well to Vogel-Tamman-Fulcher (VTF) behavior. VTF parameters and apparent activation energy were evaluated by a non-linear least square analysis. These results suggested that the solvating ability of host polymer might be a more dominating factor in improving the ionic conductivity than chain mobility.