Until recently AWS Lambda did not support PHP, but with the advent of the runtime API and layers, now we able to implement an AWS Lambda runtime in any programming language including PHP. Each layer can contain libraries, a custom runtime, or other dependencies. You can create layers, or use layers published by AWS and other AWS customers.
There is a great practical example of creating a Custom Runtime for PHP if you want to build a PHP runtime layer by yourself. In this article, we'll use partner supported PHP layer for Lambda from stackery for a quick understanding of its use.