diff --git a/lib/Service/RegistrationService.php b/lib/Service/RegistrationService.php
index 3831dec..fb5c5b0 100644
--- a/lib/Service/RegistrationService.php
+++ b/lib/Service/RegistrationService.php
@@ -354,7 +354,8 @@ class RegistrationService {
 			$this->validateDisplayname($fullName);
 		}
 
-		if ($this->config->getAppValue('registration', 'show_phone', 'no') === 'yes') {
+		if (class_exists(PhoneNumberUtil::class)
+			&& $this->config->getAppValue('registration', 'show_phone', 'no') === 'yes') {
 			if ($phone) {
 				$this->validatePhoneNumber($phone);
 			} elseif ($this->config->getAppValue('registration', 'enforce_phone', 'no') === 'yes') {
diff --git a/lib/Settings/RegistrationSettings.php b/lib/Settings/RegistrationSettings.php
index 66b0a48..97001e3 100644
--- a/lib/Settings/RegistrationSettings.php
+++ b/lib/Settings/RegistrationSettings.php
@@ -25,6 +25,7 @@ declare(strict_types=1);
 
 namespace OCA\Registration\Settings;
 
+use libphonenumber\PhoneNumberUtil;
 use OCA\Registration\AppInfo\Application;
 use OCP\Accounts\IAccountManager;
 use OCP\AppFramework\Http\TemplateResponse;
@@ -109,7 +110,7 @@ class RegistrationSettings implements ISettings {
 		// FIXME Always true when Nextcloud 22 or 21.0.1 is minimum requirement
 		$this->initialState->provideInitialState(
 			'can_show_phone',
-			method_exists($this->accountManager, 'updateAccount')
+			method_exists($this->accountManager, 'updateAccount') && class_exists(PhoneNumberUtil::class)
 		);
 		$this->initialState->provideInitialState(
 			'show_phone',