This is difficult, we don't know you, or where you live, the circumstances over the disappearances, or the age of your daughter. Because of your concern I would guess that your daughter is at school, age, about 10 - 15, and the phones are disappearing at school? And, as you are a concerned parent, I would hope that you have investigated the following possibilities, even though you may find them distasteful.
Is your daughter being bullied and giving the phone to stop it?
Is your daughter clumsy and losing the phone and is too frightened to tell you?
Is she being blackmailed? 'I saw you and Johnny behind the bike sheds playing...' well you know.
Is she selling the phones to get extra money? Please don't let it be for drugs, alcohol, or tobacco. And if the phone revenue dries up, what has she left to sell? We don't want to go that route.
There are lots of possibiliteis, I hope for yours, and especially your daughter's sake, that it is one of the simple possibilities, straight theft or loss.
I have chosen to treat this question as serious; however, there is the possibility that this is just spam to point us in the direction of the hub highlighted above?