try this...

<asp:RegularExpressionValidator ID="RegularExpressionValidator2" runat="server"
                      ControlToValidate="txtManagerMobile" ErrorMessage="Invalid Managar Mobile number!"
                      Font-Bold="True" ForeColor="Red"
      
      ValidationExpression="^(([0]{1})|([\+][4]{2}))([1]|[2]|[3]|[7]){1}\d{8,9}$" Text="*"
      ValidationGroup="ValiadtionGRP"></asp:RegularExpressionValidator>