flutter How I give my phone number in currentUser Firebase a value

Question

I tried to save the docs from the collection "users" in Firebase with a phone number but to read these docs I need to call fonction these docs with number

model.User user = model.User(
  uid: cred.user!.uid,
  userName: userName,
  portable: portable,
  nni: nni,
  email: email,
  whatsapp: whatsapp,
  photoUrl: photoUrl,
  password: password,
);

await _firestore
    .collection("users")
    .doc(portable)
    .set(user.toJson());

to read these data

Future<model.User> getUserDetails() async {
  DocumentSnapshot snap =
      await _firestore.collection('users').doc(portable).get();
  return model.User.fromSnap(snap);
}