Answer
The IUPAC name of the alkene is $3-phenylprop-1-ene$
Work Step by Step
The compound has 3 carbon atoms in its longest carbon chain containing the double bond ($prop-$). It has a $phenyl-$ substituent at position 3, and a double bond at position 1. So, the IUPAC name of the alkene is $3-phenylprop-1-ene$