There are several libraries available in PHP that provide machine learning capabilities. Some popular ones include:

1. PHP-ML: PHP-ML is a machine learning library for PHP language which aims to provide a simple and efficient way to perform common machine learning tasks. It provides implementations of various algorithms such as classification, regression, clustering, dimensionality reduction, etc.

2. FANN: FANN (Fast Artificial Neural Network Library) is a free and open-source library that implements neural networks in PHP. It provides functions to create, train, and use artificial neural networks for tasks such as pattern recognition and classification.

3. Math PHP: Math PHP is a mathematics library for PHP that provides functions for numerical analysis, linear algebra, and machine learning. It includes methods for linear regression, logistic regression, clustering, and more.

4. OpenCV-PHP: OpenCV-PHP is a PHP extension for OpenCV, an open-source computer vision library. It allows you to use OpenCV functions in PHP to perform tasks such as image recognition, object detection, and tracking.

These libraries can be installed and used in your PHP projects to implement machine learning algorithms. They provide functions and classes that make it easier to process data, train models, and make predictions. Additionally, they often have good documentation and examples to help you get started.