Mask edit validator for Phone

Currently I am using mask edit extender and validator for phone number.
My issue is if I am providing validation expression then it's treated as required filed and if i don't put validation expression then it takes incorrect value.
Below is my code.
 <asp:TextBox ID="txtContactNumber1" runat="server" Height="20px" Width="200px" ValidationGroup="Contact"></asp:TextBox>                                         <asp:MaskedEditExtender ID="txtContactNumber1_MaskedEditExtender" runat="server"                               &nbs ...