This is the 5900th most frequent Turkish word.
telefonunu
"Telefonunu" means "your phone" or "his/her/its phone" (indicating possession) in Turkish.
Here, 'telefonunu' is the object of the verb 'koy' (put), referring to 'your phone'.
Telefonunu masanın üzerine koy.
Put your phone on the table.
In this sentence, 'telefonunu' acts as the object of the verb 'kullanabilir' (can use), indicating possession ('your phone').
Telefonunu kullanabilir miyim?
Can I use your phone?
Here, 'telefonunu' refers to the friend's lost item, showing it belonged to the friend.