The PHP client is still in development. For now, you can use cURL inside your PHP code to call any algorithm:
Calling an algorithm via cURL in PHP
While most algorithms accept JSON Objects, you can also use Content-Type: text/plain for ones which require bare string input, or Content-Type: application/octet-stream for those that require a binary (such as an image file). Adjust the lines containing $data_json as needed.
Your account can make up to 80 Algorithmia requests at the same time (this limit can be raised if needed).