db.collection("users").document(FirebaseAuth.getInstance().getCurrentUser().getUid())
        .get().addOnCompleteListener(task -> {
    if(task.isSuccessful() && task.getResult() != null){
        String firstName = task.getResult().getString("First Name");
        String email = task.getResult().getString("Email");
        String phone = task.getResult().getString("Phone");
        //other stuff
    }else{
        //deal with error
    }
});