smart phone vs smartphone

smart phone and smartphone both are nouns.

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

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

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

smart phone (noun)	smartphone (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