What is the ruling on a father using a phone that has become najis due to urine, and is it considered dry and pure, and what should the questioner do in this situation?

If an impurity falls on something, and a period of time passes such that no trace of the impurity remains, neither color nor smell, then the place is judged to be pure and does not need to be washed with water. Sheikh Ibn Uthaymeen holds that if the impurity itself is removed by any means, the place becomes pure; because impurity is a filthy substance that is removed when it ceases to exist, and its its removal is not a matter of command but rather a matter of avoiding a prohibition. Thus, if a long period passes over a mobile phone that became impure, and the impurity and its traces are gone, then it is judged to be pure and it is permissible to carry it during prayer.