smartphone vs smart phone

smartphone and smart phone both are nouns.

Word	Noun	Adjective	Verb	Adverb
smartphone	Yes	No	No	No
smart phone	Yes	No	No	No

As nouns, smartphone and smart phone are synonyms defined as:

smartphone and smart phone: a mobile phone with more advanced computing capability and connectivity than basic feature phones

smartphone (noun)	smart phone (noun)
a mobile phone with more advanced computing capability and connectivity than basic feature phones	a mobile phone with more advanced computing capability and connectivity than basic feature phones