syntax vs phrase structure

syntax and phrase structure both are nouns.

Word	Noun	Adjective	Verb	Adverb
syntax	Yes	No	No	No
phrase structure	Yes	No	No	No

As nouns, syntax and phrase structure are synonyms defined as:

syntax and phrase structure: the grammatical arrangement of words in sentences

Other synonyms of syntax include sentence structure.

syntax (noun)	phrase structure (noun)
studies of the rules for forming admissible sentences	the grammatical arrangement of words in sentences
the grammatical arrangement of words in sentences
a systematic orderly arrangement