php email and phone number validation

I currently have the following working code but I need to build on to this some email and phone number validation to make sure it is an actual email and phone number not other data. I have found code to use

function valid_email($email) {
    return !!filter_var($email, FILTER_VALIDATE_EMAIL);
}

but I’m unsure how to incorporate this into my current code. I would love some help with this.

This is my current php code

//load form validate
$firstName= $_POST['firstName'];
$lastName= $_POST['lastName']; 
$address = $_POST['address'];
$phoneNumber = $_POST['phoneNumber'];
$email= $_POST['email'];
$username= $_POST['username'];
$password = sha1 ($_POST['password']);
$role = 1;


//prepare input data in an array
$userdata = array($firstName, $lastName, $address, $phoneNumber, $email, $username, $password,$role);


//prepare error list
$errors = array ();

//Validation tests and store list
if ($firstName == "" || $lastName == "" || 
    $address == "" || $phoneNumber == "" || 
    $email == "" || $username == "" || 
    $password == "" || $role == "" ) {
    array_push($errors, "All form fields must be filled out before submitting.");
}

//if errors redirect back to form page and save attempted data.
if (count($errors) > 0) {
    $_SESSION['userdata'] = $userdata;
    $_SESSION['errors'] = $errors;
    header("Location: ../register.php");
}else{
    unset($_SESSION['userdata']);
    unset($_SESSION['errors']);
    $query = "INSERT INTO customers (firstName, lastName, address, phoneNumber, email, username, password) VALUES ('$firstName','$lastName', '$address', '$phoneNumber', '$email', '$username', '$password')";

    //die (print_r($query));
    if (mysqli_query($mysqli, $query)) {
        $last_id = $mysqli->insert_id;
        $query2 = "INSERT INTO users_in_roles (userID, roleID) VALUES ('$last_id', 1);";

        if ($mysqli->query($query2)) {
            header("Location: ../Login.php");
        }else {
            die(print_r($mysqli->error));
        }
    }
}

Answer

This is one example.
I made a foreach with an array just to show you both outputs.

$email = ["[e-mail]","abc@gmailcom"];
foreach ($email as $e){
    if (filter_var($e, FILTER_VALIDATE_EMAIL)) {
        echo "valid";
    } else {
        echo "not valid";
    }
}

https://3v4l.org/GcKRp

In your case you should probably have it after you check if any of the fields are empty:

if ($firstName == "" || $lastName == "" || 
        $address == "" || $phoneNumber == "" || 
        $email == "" || $username == "" || 
        $password == "" || $role == "" ) {
    array_push($errors, "All form fields must be filled out before submitting.");
}

if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    array_push($errors, "Email is not valid.");
}

$phone = "11-331-11111";
$phone = preg_replace("/[^d]/", "", $phone);
if (strlen($phone) <= 10) { 
    array_push($errors, "Phone not valid.");
}

Removes non digits and checks if length is less than or equal to 10.