If he knows that the alcohol which is added to the flavoring is naturally a liquid intoxicating agent, then it is not permissible to consume it, since such addition makes the flavor Najis, and thus, makes the food Najis and it is prohibited to consume Najis food. If he does not know if the added substance is Najis, then it is permissible to consume the food.
As long as you are not sure that your hand was najis when you touched the mobile phone, you can consider it as tahir. Furthermore, najasah is transferred from one thing to another if the dampness in one of them is transferred to the other. If the mobile phone does become najis, then it cannot be purified again except with water. It is not prohibited to use it while it is najis.
If he did not know that deliberately staying in the state of Janaba until dawn nullifies the fast, then it is valid.It is also valid if he did not know that he was in the state of Janaba until after dawn when he realized it.