This is the 6202nd most frequent Korean word.
스마트폰을
"스마트폰을" means "smartphone" (object form).
In this sentence, '스마트폰을' is the direct object of the verb '사용합니다', meaning 'to use'.
저는 저녁식사 후에 스마트폰을 사용합니다.
I use the smartphone after dinner.
Here, '스마트폰을' indicates the object that was left behind, showing possession or involvement in the action described.
스마트폰을 두고 와서 다시 돌아갔습니다.
I left the smartphone behind and went back to get it.
In this usage, '스마트폰을' is again the direct object of the action '보여줬어요', meaning 'to show'.