zlib compression

Have you already enabled Gzip compression via mod_deflate? If so, this isn’t necessary although it is recommended to enable compression on your origin server of course.

If you use TLS, no. And you should use TLS.

There are several different exploits that allow TLS communication to be deciphered when compression is used.

For many types of communication it does not matter, but it really is best practice to just not use compression for dynamic content.

For purely static content, compression is fine, but that’s not PHP.