Multiple validation controls for a text box

I have a TextBox with two validation controls connected to it:

        <asp:TextBox ID="txtBillPhoneNumber" runat="server"></asp:TextBox>
        <asp:RequiredFieldValidator ID="rfvBillPhoneNumber" runat="server"
            ControlToValidate="txtBillPhoneNumber"
            ErrorMessage="Billing phone number is a required field."
            Text="*"></asp:RequiredFieldValidator>
        <asp:RegularExpressionValidator ID="revBillPhoneNumber" runat="server"
            ControlToValidate="txtBillPhoneNu ...