Phosphate glasses incorporating large concentrations of Eu3+ ions are of interest for optical applications as their distinct red-emitting character resists deterioration with increasing Eu3+ content. Still, the low propensity for concentration quenching in these is not well understood, and thus evaluations linking structural, thermal, and optical properties with Eu3+ content are desired. In this work, 50P2O5-(50 - x)BaO-xEu2O3 (x = 0, 1, 2, 4, 6 mol %) glasses pertinent to photonics were prepared by melt-quenching and further scrutinized with regards to the composition-structure-property relationship. A comprehensive experimental investigation was carried out encompassing density and basic physical properties, X-ray diffraction (XRD), Raman scattering, dilatometry, differential scanning calorimetry (DSC), optical absorption, and photoluminescence (PL) spectroscopy with emission decay analysis. The data from six techniques are in strong agreement with the existence of a critical Eu2O3 concentration which divides the studied concentration range into two sections: (1) lower concentrations, up to about 2.5 (±0.1) mol %, with predominantly long-range (LR) effects of the modifier electrostatic field and (2) higher dopant concentrations, with predominantly short-range (SR) effects of the modifier field. The authors propose that LR interactions lead to shortening of the P-tetrahedral chains, while the SR interactions are expressed in increasing the covalent character of the bonds between the nonbridging oxygens and Eu3+ ions. Concentration correlations between diverse macroscopic data sets, such as densitometry, dilatometry, Raman scattering, calorimetry, and PL, concur synergistically, elucidating the microscopic physical LR-SR interplay between glass network former and the cationic electrostatic field of the modifiers.