Manipulating the distribution of rare earth activators in multiple cations' sites of phosphor materials is an essential step to obtain tunable emission for the phosphor-converted white-light-emitting diodes (pc-WLEDs). However, it remains the challenge to realize the photoluminescence tuning in the single-phased phosphor with single activator, due to the uncertain location of doped ions and adjustable crystallographic sites. Herein we reported the beta-Ca-3(PO4)(2)-type solid solution phosphors (Ca8.98-xSrx)MgK(PO4)(7):2%Eu2+ (x = 0-8.98) and the effects of replacing Ca2+ by Sr2+ ions on the phase structures and color-tunable emission were investigated in detail. Tunable color emission has been realized by manipulating the redistribution of Eu2+ ions among different cation sites with adjustable chemical environment, and the related mechanism on the local structures has been discussed. The high R-a (85) and low color temperature (CCT) (4465 K) values of the as-fabricated WLEDs lamp indicate that (Ca4.98Sr4)MgK(PO4)(7):2%Eu2+ can act as a promising white-emitting phosphor for single-phased pc-WLEDs. This work provides a new insight into the tuning of the compositions and multiple activator sites toward single-phased white emission.