This study investigated the effects of dephosphorylation and sodium hexametaphosphate (SHMP) salt addition on the viscosity of milk protein concentrate (MPC) solutions. Dephosphorylation (DP) of casein was performed using bovine alkaline phosphatase. Nuclear magnetic resonance (NMR) spectra showed that dephosphorylation depleted the casein-bound phosphate region (CNP). SHMP addition (5 mM) had no impact on the 31P NMR spectra of DP-MPC; addition of 5 mM SHMP to control MPC (C-MPC) resulted in a shift in peaks associated with the CNP region, possibly caused by SHMP sequestering calcium, leading to swelling of micelles. DP-MPC exhibited a lower viscosity compared to C-MPC, with SHMP addition at 12.5 and 25 mM causing gelation of C-MPC and DP-MPC solutions. This work confirmed the role that phosphate residues have in maintaining micelle structural stability and provides new insights into controlling viscosity of MPC solutions.