designer.vb does not save changes to Partial Public Class

Delete the designer.vb page, right click on the aspx page and choose Convert to Web Application.

Formatting a phone number in ASP.NET

<asp:Label ID="Label1" runat="server" Text='<%# String.Format("{0:(###) ###-####}", Convert.ToInt64(DataBinder.Eval(Container.DataItem,"PhoneNo"))) %>'></asp:Label>