Apparently, there are no official examples of caching in PHP.  
 Retrieve secrets from AWS Secrets Manager - AWS Secrets Manager
 Caching mechanism for PHP - Issue #15 - aws/aws-secretsmanager-caching-python
I found an example of caching in PHP on Stack Overflow, but I'm not familiar with PHP, so I'm not sure if this will meet your requirements. 
 php - F3 Framework: how to make sure that caching is working correctly?
I hope this is helpful.
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