User Input Validation - Client & Server - in C#.NET

<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="textEmail" Display="Dynamic" ErrorMessage="Email Address is Required" ValidationGroup="AllValidators">*</asp:RequiredFieldValidator>
Email:
<asp:TextBox ID="textEmail" runat="server"></asp:TextBox> 
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="textEmail" Display="Dynamic" ErrorMessage="Email Address must be in the format abc@xyz.abc" ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*" ValidationGroup="AllValidators">Invalid Format</asp:RegularExpressionValidator><br />

<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="textNumberInParty" ErrorMessage="Number in Party is Required" ValidationGroup="AllValidators">*</asp:RequiredFieldValidator>
Number in Party:
<asp:TextBox ID="textNumberInParty" runat="server" Width="45px"></asp:TextBox> 
<asp:RangeValidator ID="RangeValidator1" runat="server" ControlToValidate="textNumberInParty" Display="Dynamic" ErrorMessage="Please enter 1-20 for the number of people in your party" MaximumValue="20" MinimumValue="1" Type="Integer" ValidationGroup="AllValidators">Enter a number between 1 and 20</asp:RangeValidator><br />

<asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="textPreferredDate" Display="Dynamic" ErrorMessage="Date is Required" ValidationGroup="AllValidators">*</asp:RequiredFieldValidator>
Preferred Date:
<asp:TextBox ID="textPreferredDate" runat="server"></asp:TextBox>
<asp:CustomValidator ID="CustomValidator1" runat="server" ControlToValidate="textPreferredDate" Display="Dynamic" ErrorMessage="Format: m/d/yyyy" OnServerValidate="CustomValidator1_ServerValidate" ValidationGroup="AllValidators" ClientValidationFunction="validateDate">Invalid format (m/d/yyyy)</asp:CustomValidator><br />

<asp:RequiredFieldValidator ID="validatorRequiredPhoneNumber" runat="server" ControlToValidate="textPhoneNumber" Display="Dynamic" ErrorMessage="You must provide a phone number">*</asp:RequiredFieldValidator>
<asp:CheckBox ID="checkPhoneConfirmation" runat="server" AutoPostBack="True" OnCheckedChanged="checkPhoneConfirmation_CheckedChanged" Text="Confirm Reservation by Phone" /><br />
Tel. No.
<asp:TextBox ID="textPhoneNumber" runat="server" Enabled="False"></asp:TextBox> 
<asp:RegularExpressionValidator ID="validatorRegExPhoneNumber" runat="server" ControlToValidate="textPhoneNumber" Display="Dynamic" ErrorMessage="Phone number format is invalid" ValidationExpression="((\(\d{3}\) ?)|(\d{3}-))?\d{3}-\d{4}">Invalid Format</asp:RegularExpressionValidator><br />
<asp:Button ID="buttonSubmit" runat="server" OnClick="buttonSubmit_Click" Text="Submit" ValidationGroup="AllValidators" /><br />
<asp:Label ID="labelResponse" runat="server"></asp:Label><br />
<asp:ValidationSummary ID="ValidationSummary1" runat="server" ValidationGroup="AllValidators" />

labelResponse.Text = "";

if (Page.IsValid)
{ }
else
{ }

try
{ }
catch
{ }

{ }
else
{ }

var iDay, iMonth, iYear;
var arrValues;
arrValues = args.Value.split("/");
iMonth = arrValues[0];
iDay = arrValues[1];
iYear = arrValues[2];

var testDate = new Date(iYear, iMonth - 1, iDay);
if ((testDate.getDate() != iDay) || { }

return true;