In-phase　coherently　coupled　proton-implantdefined　vertical　cavity　surfaceemitting　laser　(VCSEL)　arrays　face　difficulties　in　current　spreading,　resulting　in　small　array　scale,　low　output　power,　and　broad　beamwidth.　Although　patterned　metal　grids　can　improve　the　current　spreading,　the　undesirable　out-of-phasemode　tends　to　be　dominant　in　the　array.　In　this　letter,　by　means　of　engineering　the　implantation　and　array　parameters,　in-phase　mode　is　obtained　in　large-scale　proton-implant-defined　arrays　with　metal　grids.　Experimental　results　showthat　these　arrays　are　operating　in　in-phasemode　with　a　nominal　interelement　spacing　of　8　mu　m　and　an　implantation　depth　of　2.22　mu　m.　By　using　these　parameters,　a　5x5　in-phase　array　with　a　narrow　beamwidth　(far-field　full　width　at　half　maximum)　of　1.61　degrees　is　realized.　Besides,　a　10x10　in-phase　array　with　a　beamwidth　of　1.89　degrees　and　an　output　power　of　10.25　mW　for　the　in-phase　mode　is　achieved.　The　calculation　of　far　fields　is　performed　to　confirm　the　in-phase　operation　measured　results.　Such　a　simple　and　low-cost　technology　provides　a　promising　method　for　preparing　large-scale　in-phase　coherently　coupled　VCSEL　arrays.