$\text{ The geometry of }\mathrm{Ni}(\mathrm{CO}{)}_4\text{ and }\mathrm{Ni}{\left(\mathrm{P}{\mathrm{Ph}}_3\right)}_2{\mathrm{Cl}}_2\text{ are }$

In $\left[\mathrm{Ni}(\mathrm{CO}{)}_4\right]\mathrm{CO}$ is a strong field ligand pairing of electrons in Ni atoms results sp³ hybridisation.

In $\mathrm{Ni}{\left(\mathrm{P}{\mathrm{Ph}}_3\right)}_2{\mathrm{Cl}}_2$ due to the bulky P Ph³ ligand it prefers sp³ hybridisation to minimize repulsions