small beer vs physical object

small beer and physical object both are nouns.

Word	Noun	Adjective	Verb	Adverb
small beer	Yes	No	No	No
physical object	Yes	No	No	No

As nouns, physical object is a hypernym of small beer; that is, physical object is a word with a broader meaning than small beer:

small beer: something of small importance
physical object: a tangible and visible entity; an entity that can cast a shadow

Other hypernyms of small beer include object.

small beer (noun)	physical object (noun)
something of small importance	a tangible and visible entity; an entity that can cast a shadow