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 you live with your father as a dependent, similar to the wife living with her husband or the child with his mother, then you consider the area that your father considers as hometown as your hometown too. However, if you are independent from your father in terms of residence, then your hometown is where you live with stability in such a way you consider it as your hometown.