diff --git a/composer.json b/composer.json
index b986e5c..0724fd5 100644
--- a/composer.json
+++ b/composer.json
@@ -61,6 +61,7 @@
 		"php": ">=8.0",
 		"ext-json": "*",
 		"automattic/jetpack-autoloader": "^3.0",
+		"giggsey/libphonenumber-for-php": "^8.13",
 		"justinrainbow/json-schema": "^5.2",
 		"pronamic/wp-http": "^1.2",
 		"pronamic/wp-mollie": "^1.6",
diff --git a/src/AddressTransformer.php b/src/AddressTransformer.php
index 625e29e..9ba29f8 100644
--- a/src/AddressTransformer.php
+++ b/src/AddressTransformer.php
@@ -10,6 +10,8 @@
 
 namespace Pronamic\WordPress\Pay\Gateways\Mollie;
 
+use libphonenumber\PhoneNumberFormat;
+use libphonenumber\PhoneNumberUtil;
 use InvalidArgumentException;
 use Pronamic\WordPress\Mollie\Address as MollieAddress;
 use Pronamic\WordPress\Pay\Address as WordPressAddress;
@@ -61,8 +63,12 @@ public function transform_wp_to_mollie( WordPressAddress $address ): MollieAddre
 
 		$mollie_address = new MollieAddress( $given_name, $family_name, $email, $street_and_number, $city, $country );
 
+		$phone_util = PhoneNumberUtil::getInstance();
+
+		$phone_number_object = $phone_util->parse( $address->get_phone(), $country );
+
 		$mollie_address->organization_name = $address->get_company_name();
-		$mollie_address->phone             = $address->get_phone();
+		$mollie_address->phone             = $phone_util->format( $phone_number_object, PhoneNumberFormat::E164 );
 		$mollie_address->street_additional = $address->get_line_2();
 		$mollie_address->postal_code       = $address->get_postal_code();
 		$mollie_address->region            = $address->get_region();