PHP Version 7.3.22 to be removed in future macOS
php -v gives the following response:
WARNING: PHP is not recommended  
PHP is included in macOS for compatibility with legacy software.  
Future versions of macOS will not include PHP.

The release notes for Catalina contain the following remark:
https://developer.apple.com/documentation/macos-release-notes/macos-catalina-10_15-release-notes

Scripting Language Runtimes
Deprecations
Scripting language runtimes such as Python, Ruby, and Perl are included in macOS for
compatibility with legacy software. Future versions of macOS won’t
include scripting language runtimes by default, and might require you
to install additional packages. If your software depends on scripting
languages, it’s recommended that you bundle the runtime within the
app.

In short: macOS continues to include 'legacy' versions of things like Python, Ruby, Perl, and indeed PHP, so that existing code won't break, but Apple is leaving it to the user to install the versions that they want to use.
At the time of writing, 10.16 ('macOS 11') continues to include these languages.