How is the numbering in phenylpropenes?
Obviously, there are three carbons in propene to which a phenyl group might be attached. Let's have a look and name the compounds:



1 with the phenyl group at C-2 of propene is 2-phenylpropene, also known as $\alpha$-methylstyrene.

2 with the phenyl group at C-1 of propene is 1-phenylpropene. To be exact, the compound drawn is (E)-1-phenylpropene. E is for entgegen, that is on opposite sides of the double bond.

3 is 3-phenylpropene, also known as allylbenzene.