Batch does not provide a library for PHP at this point but Batch provides REST APIs you can use to send push notifications to your userbase or specific user IDs:
Push Campaigns API: Made for 1-to-many interactions. It allows you to send push notifications in mass to your users according to targeting criteria (using your custom data or Batch generated data) or with your own segmentation engine with Custom Audiences.
Transactional API: Made for 1-to-1 or 1-to-few interactions. It allows you to send push notifications to a specific list of user IDs (push token or Custom User IDs) based on events in your back-end (e.g. "You have a new friend request").