Ae, pololei. The verb "put" should not be separated from its preposition "back" by the direct object "the phone." The prepositional verb "put back" should be the correct answer. Note that other prepositional verb phrases in ths lesson -- "turn on the light" and "turn off the light" -- are correct. Why not this?
Yes to what Jessi784299 said, and to further the clarification.... If I were to say "E hoʻi hoʻi ʻoe ke kelepona", I would be telling, you, the telephone, to return to where you came from. So the "i" tells that in "E hoʻihoʻi ʻoe i ke kelepona," I am asking you to put the phone back.
I'm not much better in English, but if you have the word 'oe in the sentence you should translate the 'you' accordingly. Shouldn't you? If we are having a conversation with someone it's already understood who u talking about.. sometimes the app makes mistakes, but i still like.
E kala mai, sorry for the late response -- but yes, you could simply say "E hoʻi hoʻi i ke kelepona" to the person you are talking to. But in Duolingo, the app is teaching you how to differentiate between ʻoe, olua, okou, and ia, lāua, lākou. Sort of like in Spanish you have tu, usted, ustedes, el, ella, ellos and ellas etc. :)