Step 1: Identify reagent nature.
PhMgBr is a Grignard reagent, behaves as \(\text{Ph}^-\) nucleophile.
PCl\(_3\) is electrophilic at phosphorus. Step 2: Substitution of Cl atoms by phenyl group.
Each chloride in PCl\(_3\) can be replaced by phenyl group from Grignard reagent.
So overall:
\[
PCl_3 + 3PhMgBr \rightarrow PPh_3 + 3MgBrCl
\] Step 3: Product formed.
The product is triphenylphosphine (PPh\(_3\)). Final Answer:
\[
\boxed{\text{(C) triphenylphosphine}}
\]