The Eighteen Electron Rule has not been used correctly, because this gives only 14 electrons. There is no P-P bond in this compound. The phosphorous in the in the tertiaryphosphine ligand (PR3) bonds only to the metal so both of the electrons in its lonepair go to Pt.
Pt = 10e- Br = 1e- C6H5 = 1e- (Pr3P)2 = 2e- 14e- |