I think you may be getting this record ,so before using setText make sure values are not null and values which you are retriving doesnt match i.e
{"result":[{"Firstname":null,"Lastname":null,"Phoneno":null}]}
String f_name = Data.getString("First_name");//it should be Firstname
String l_name =Data.getString("Last_name");//it should be Lastname
String phone_no = Data.getString("Phone_no");//it should be Phoneno
if(f_name!=null){
Firstname.setText(f_name);
}
if(l_name!=null){
Lastname.setText(l_name);
} if (phone_no!=null){
Phoneno.setText(phone_no);
}