validation

<!doctype html>
<html>
    <head>
        <title>Update Phone Nr.</title>
    </head>
    <body><?php

$employeeNumber = filter_input(INPUT_POST, 'EmployeeNumber');
$officePhone = filter_input(INPUT_POST, 'OfficePhone');

if (!isset($_POST['Find'])) { //check if form has been submitted
    header("Location: index.php"); // if not, redirect to index.php
    die();
}

$errorCount = 0;

$validId = validID($employeeNumber);
$validPhone = validPhoneNum($officePhone);

if ($validId && $validPhone) {
    echo "<p>Thank you. Employee $validId's number has been updated to $validPhone</p>";
} else {
    echo "<p>Please use the \"Back\" button to re-enter the data.</p>";
}
?></body>
</html><?php

function validPhoneNum($phone_raw) {

    $phone = stripcslashes(trim($phone_raw));
    if (strlen($phone) !== 10) {
        echo "<p>please enter a valid 10 digit phone number</p>";
        return false;
    } else if (is_numeric($phone) == false) {
        echo "<p>phone number must only contain numbers</p>";
        return false;
    }
    return $phone;
}

function validID($id_raw) {

    $id = stripcslashes(trim($id_raw));
    if (empty($id)) { //check if Employee Number field is blank
        echo "<p>You must enter an employee Number</p>"; //if blank display message
        return false;
    }
    return $id;
}