Cloud watch application insight supports PHP application monitoring

Hello.

As far as I can see from the document below, I don't think PHP is mentioned.
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/appinsights-what-is.html#appinsights-stack

Is it possible to access your PHP application from a public network?
In that case, I think it would be a good idea to use CloudWatch Synthetics to set up external monitoring.
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries.html

I assume this is a PHP web application on EC2 Linux instance.

You can install CloudWatch agent and use it to collect Linux metrics and logs (e.g. php error log and web server logs which contains information such as URLs requested, duration of each request, http status code etc..).

If you need to collect custom PHP application metrics, you can install AWS SDK for PHP and modify your PHP code to publish custom metrics to CloudWatch.