How to use LINQ for searching a datatable with some row deleted?

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C#

LINQ

I have a datatabel, in which I want to find any duplicated record(for example, the mobile phone number). I use following code in LINQ:

var list_mobile = dataTable_QueryResult.Rows.OfType<DataRow>().Select(x => x["mobile"].ToString());
var q_mobile = from x in list_mobile
           group x by x into g
           let count = g.Count()
           orderby count descending
           select new { Value = g.Key, Count = count };

foreach (var x in q_mobile)
{
    if (x.Count > 1)
    {
        Label_Alarm.Visible = true;
    }
}

It comes an error when some rows have been deleted - visiting the row that has been deleted. I want to use the Where() command to exclude those deleted rows, but I don't know how to code it in LINQ? Could anyone help me this ? Thanks!