Why is the organic compound $\ce{C_6H_5−CH=CH−CH_2Cl}$ named 3-chloro-1-phenylprop-1-ene and not 9-chloronon-5,7-dien-2,4-yne even though there is no specification whatsoever that there is a phenyl group in the organic molecule?

$\ce{C_6H_5−CH=CH−CH_2Cl}$
 
can also be written as

$\ce{CH#C-C#C-CH=CH-CH=CH-CH_2-Cl}$

and the name for this organic compound would be 9-chloronon-5,7-dien-2,4-yne.
How do we surely know that there exists a phenyl group in the molecule?   
Also why is phenyl treated as a substituent and cannot be considered in the longest chain?