Basic form with php validation

queries.php

<?php
/**
 * The template used for displaying the queries form
 *
 * @package hostel_mama
 */
?>
<?php
	$error_query_name = false;
	$error_query_email = false;
	$error_query_phone = false;
	$error_date_res = false;
	$error_res_num = false;
	$error_query = false;

	if (isset($_POST['queries-submit'])) {
		// Initialize the variables
		$query_name = '';
		$query_email = '';
		$query_phone = '';
		$date_res = '';
		$res_num = '';
		$query = '';
		
	
		if (trim($_POST['query-name']) === '') {
			$error_query_name = true;
		} else {
			$query_name = trim($_POST['query-name']);
		}
		
		if (trim($_POST['query-email']) === '' || !isEmail($_POST['query-email'])) {
			$error_query_email = true;
		} else {
			$query_email = trim($_POST['query-email']);
		}

		if (trim($_POST['query-phone']) === '') {
			$error_query_phone = true;
		} else {
			$query_phone = trim($_POST['query-phone']);
		}

		if (trim($_POST['date-res']) === '0') {
			$error_date_res = true;
		} else {
			$date_res = trim($_POST['date-res']);
		}
		
		if (trim($_POST['res-num']) === '') {
			$error_res_num = true;
		} else {
			$res_num = stripslashes(trim($_POST['res-num']));
		}

		if (trim($_POST['query']) === '') {
			$error_query = true;
		} else {
			$query = trim($_POST['query']);
		}
		
		// Check if we have errors
		if (!$error_query_name && !$error_query_email && !$error_query_phone && !$error_date_res && !$error_res_num && !$error_query) {
			// Get the receiver email from the WP admin panel 
			// change after initial testing! 
			$receiver_email = get_field('queries_e-mail');

			$subject = "Message de $query_name";
			$body = "Vous avez un nouveau message de la part de $query_name" . PHP_EOL;
			$body .= "Date de r&eacute;servation: $date_res" . PHP_EOL;
			$body .= "Num&eacute;ro de r&eacute;servation: $res_num" . PHP_EOL;
			$body .= "Vous pouvez le contacter $query_name via email à $query_email or  par t&eacute;l&eacute;phone &agrave; $query_phone.". PHP_EOL;			$body .= PHP_EOL;
			$body .= "Message: $query" . PHP_EOL .
			$body .= PHP_EOL;
			
			$headers = "From: $query_email" . PHP_EOL;
			$headers .= "Reply-To: $query_email" . PHP_EOL;
			$headers .= "MIME-Version: 1.0" . PHP_EOL;
			$headers .= "Content-type: text/plain; charset=utf-8" . PHP_EOL;
			$headers .= "Content-Transfer-Encoding: quoted-printable" . PHP_EOL;

			// If all is good, we send the email
			if (mail($receiver_email, $subject, $body, $headers)) {
				$query_email_sent = true;
			} else {
				$query_email_sent_error = true;
			}
		}
	}

?>


				    
				    
				    <?php if (isset($query_email_sent) && $query_email_sent == true) : ?>
					<div data-alert class="alert-box success">
					<p><?php _e('Thank you.', 'hostel_mama' );?></p>
					<p><?php _e('We will respond to your message as quickly as possible.', 'hostel_mama' );?></p>
					</div>
				
				<?php elseif (isset($query_email_sent_error) && $query_email_sent_error == true) : ?>
					
					<div data-alert class="alert-box alert">
					<p><?php _e('There was an error!', 'hostel_mama' );?></p>
					<p><?php _e('Unfortunately, there was an error while trying to send the email. Please try again.', 'hostel_mama' );?></p>
					</div>
					
				<?php else : 
					$url= 'index.php?page_id=10';
					$string= sprintf(__('Please check our <a href="%1$s"><abbr title="Frequently asked questions">FAQ </abbr> page</a> before submitting this form. You will likely find the answer there.', 'hostel_mama'), esc_url( $url ) );
				?>
					
				    <div class="panel">
				    	<p><?php echo $string ?></p> 
				    </div>
				    <form method="post" action="<?php the_permalink(); ?>" data-abide>
				    
				    <fieldset>
				    <div class="row"> 
				     <div class="large-6 columns">
					    <label for="query-name"><?php _e('Full name: ', 'hostel_mama' )?></label>
					    <input id="query-name" name="query-name" type="text" required pattern="[a-zA-Z]+"/>
					    <small class="error"><?php _e('Name is required and must be composed of letters.', 'hostel_mama' )?></small>
					    
					    <label for="query-email"><?php _e('Email address: ', 'hostel_mama' )?></label>
					    <input id="query-email" name="query-email" type="email" required /> 
					    <small class="error"><?php _e('An email address is required.', 'hostel_mama' )?></small>
					                    
					    <label for="query-phone"><?php _e('Phone: ', 'hostel_mama' )?></label>
					    <input id="query-phone" name="query-phone" type="tel" />
					    
					    
					    <div class="row">
						    <div class="large-6 columns">
						    <label for="date-res"><?php _e('Date of stay or reservation: ', 'hostel_mama' )?></label>
						    <input id="date-res" name="date-res" type="date" />
						    </div>
						    <div class="large-6 columns">
						    <label for="res-num"><?php _e('Reservation number: ', 'hostel_mama' )?></label>
						    <input id="res-num" name="res-num" type="number" />
						    </div>
					    </div>
					 </div>             
				    <div class="large-6 columns">
				    	<label for="query"><?php _e('Message or Query: ', 'hostel_mama' )?></label>
				    <textarea id="query" name="query" class="lrg-txtarea" cols="30" rows="10"></textarea>
				    <small class="error"><?php _e('You forgot to include a message.', 'hostel_mama' )?></small>
				    </div>
				    <input type="hidden" id="queries-submit" name="queries-submit" value="true" />     
				    <input type="submit" class="button success radius">
				    <input type="reset" class="button alert radius"/>

</div>				      </fieldset>
				    </form>
	<?php endif; ?>