# Omission of locants for functional groups in IUPAC names

I'm having a bit of conflict while naming molecules as per IUPAC the nomenclature rules. If we take the following compound for example,

IUPAC would say that that correct name is 2-phenylacetaldehyde. But then for this molecule,

IUPAC designate it the name is chloroacetaldehyde.

Why does the aldehyde with a benzene ring as a functional group receive a '2' while the aldehyde with a halide as a functional group does not? I figured the molecules mentioned above wouldn't require a number to designate their functional groups given they're both substituents to an ethane parent chain.

Also, would it be acceptable to drop 'aldehyde' and replace it with 'ethanal'. I've always been taught to add '-al' with a '-CHO' functional group?

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