Update phone validation regex to accept only numbers and correct amount - Fix "must consist of only numbers" validation error message to be specific

mailchimp.php

@@ -1046,26 +1046,55 @@ function mailchimp_sf_merge_submit( $mv ) {
  *
  * @param array $opt_val Option value
  * @param array $data Data
- * @return void
+ * @return array|WP_Error
  */
 function mailchimp_sf_merge_validate_phone( $opt_val, $data ) {
-	// This filters out all 'falsey' elements
+	// Filter out falsy values
 	$opt_val = array_filter( $opt_val );
-	// If they weren't all empty
+
+	// If they were all empty
 	if ( ! $opt_val ) {
-		return;
+		return $opt_val;
 	}
 
+	// Trim whitespace
+	$opt_val = array_map( 'trim', $opt_val ); // Beginning and end
+	$opt_val = array_map( fn( $s ) => preg_replace( '/\s/', '', $s ), $opt_val ); // Middle
+
+	// Format number for validation
 	$opt_val = implode( '-', $opt_val );
-	if ( strlen( $opt_val ) < 12 ) {
-		$opt_val = '';
-	}
 
-	if ( ! preg_match( '/[0-9]{0,3}-[0-9]{0,3}-[0-9]{0,4}/A', $opt_val ) ) {
-		/* translators: %s: field name */
-		$message = sprintf( esc_html__( '%s must consist of only numbers', 'mailchimp' ), esc_html( $data['name'] ) );
-		$error   = new WP_Error( 'mc_phone_validation', $message );
-		return $error;
+	switch ( true ) {
+		/**
+		 * Phone number must be 12 characters long
+		 * 10 digits [0-9] and 2 dashes "-"
+		 */
+		case strlen( $opt_val ) < 12:
+			$message = sprintf(
+				/* translators: %s: field name */
+				esc_html__( '%s must contain the correct amount of digits', 'mailchimp' ),
+				esc_html( $data['name'] )
+			);
+			$opt_val = new WP_Error( 'mc_phone_validation', $message );
+			break;
+
+		/**
+		 * Phone number must consist of only numbers
+		 */
+		case ! preg_match( '/^[0-9]{3}-[0-9]{3}-[0-9]{4}$/', $opt_val ):
+			$message = sprintf(
+				/* translators: %s: field name */
+				esc_html__( '%s must consist of only numbers', 'mailchimp' ),
+				esc_html( $data['name'] )
+			);
+			$opt_val = new WP_Error( 'mc_phone_validation', $message );
+			break;
+
+		/**
+		 * No issues, pass validation
+		 */
+		default:
+			break;
 	}
 
 	return $opt_val;