By altering the monodentate phosphine ligand (PR3), a series of charge‐neutral OsII complexes 1a–5a [Os(fppz)2(PR3)2] and 1b–5b [Os(L‐NPh)(PR3)2] [fppz = 3‐(trifluoromethyl)‐5‐(2‐pyridyl)pyrazole; PR3 = PMe3 (1a/1b), PPhMe2 (2a/2b), PPh2Me (3a/3b), PPh3 (4a/4b), P(OPh)3 (5a/5b); L‐NPh is two bis(pyridylpyrazolate] fragments connected by a phenylamino bridge at the 6‐position of the pyridyl rings] have been investigated by density functional theory (DFT) methods. The P(OPh)3 substitution in 5a (5b) rendered a considerable stabilization to the HOMO energy levels and an enlargement of the HOMO–LUMO energy gap compared with those of 1a–4a (1b–4b), which led to a clear blueshift in the emission spectra. With the enhancement of the electron‐withdrawing strength of the phosphine ligands, the emissions are successively blueshifted from 1a/1b to 4a/4b. The results also revealed a general relationship between the variations of the emissions and changes to the Os–P bond lengths. The phenylamido bridge in 1b–5b redshifted the absorption and emission spectra compared with those of 1a–5a and decreased the Os(d) participation in the HOMOs, which led to dominant L‐ligand‐based 3π–π* character for their emissive states compared with dominant metal‐to‐ligand charge‐transfer (3MLCT) characters for 1a–5a.