Answer
4-phenylbut-1-yne
Work Step by Step
It is called 4-phenylbut-1-yne because there is a four carbon chain with a triple bond at the first carbon, so but-1-yne. Since there is a phenyl group on the 4th carbon, its 4-phenylbut-1-yne. Phenyl group has a lower priority than a triple bond (alkyne).