How to retrieve all row of one column in firebase flutter

Hi, I am trying to make a firebase database call to retrieve all row of one particular column in the firebase database and display it in a textbox in my flutter app.
I have a piece of code I tried to modify to access the database as below:

void _getPhoneNos(BuildContext context) async {

fb.Database db = fb.database();

DatabaseReference dataRef = db.ref('table') as DatabaseReference;

dataRef.onValue.listen((event) {

  DataSnapshot snapshot = event.snapshot;

  if (snapshot == null) {

    print("Result is Empty");

    return;

  }

Map<dynamic, dynamic> tableInfo = snapshot.val();

Please, I wish to get the table info that contain users info and select all the row of one column (phone), that is, selecting only phone numbers of all the users and display them on a textbox in my flutter app…

Any help, as a I am still new to flutter.