Phillip wasn't speaking to a baby, nor was he speaking of babies. You're trying to create general doctrine from a specific instance which doesn't necessarily apply.
Sure it applies...The command is always, REPENT and be baptized...Babies don't repent...
Mar 16:16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
If you believe not, you will be damned...Doesn't say a word about being damned for not being baptized...