// Startup
myTable.Rows.Add(ref this.missing);
myTable.Rows.Last.Cells[1].Range.Text = "Phone:";
myTable.Rows.Last.Cells[2].Select();
PlainTextContentControl ptcc;
ptcc = this.Controls.AddPlainTextContentControl("Phone");
ptcc.Title = "Phone";
ptcc.PlaceholderText = "Enter your phone here";
ptcc.LockContentControl = true;

// Button_Click
PlainTextContentControl ptcc;
foreach (object ctrl in this.Controls)
{
   ptcc = ctrl as PlainTextContentControl;
   if ((ptcc != null) && (ptcc.Title == "Phone"))
   {
       ptcc.LockContentControl = false;
       this.Controls.Remove(ptcc);
       break;
   }
}

The above code runs without error, but the PlainTextContentControl is not
removed.  Investigated it and found that the dynamic content control is not
a member of this.Controls collection!!!  How to remove it in code?