Truffle is an integration layer for interpreted languages in GraalVM. The canonical Truffle language included in the Graal distribution is GraalJS, a replacement for the now deprecated Nashorn JavaScript engine for the JVM. Similarly, TruffleRuby is an alternative to JRuby and GraalPython is an alternative to Jython. Neither of these Truffle implementations has gained traction and they will not until they fully implement the main frameworks for each ecosystem (Ruby on Rails and Django/NumPy respectively).
The same will hold true for a Truffle implementation of PHP. It will need to support the C interface components like PDO database drivers and the Laravel web framework.
The linked project was created as part of a graduate thesis and demonstrates the feasibility of GraalVM/Truffle as a performant polyglot platform. I'm not convinced that Ruby/Python/PHP integration with Java Bytecode is an important use case moving forward. It could have been when Rails/Django/Laravel were on top of the web framework game but the demand for this use case is diminishing.
The same will hold true for a Truffle implementation of PHP. It will need to support the C interface components like PDO database drivers and the Laravel web framework.
The linked project was created as part of a graduate thesis and demonstrates the feasibility of GraalVM/Truffle as a performant polyglot platform. I'm not convinced that Ruby/Python/PHP integration with Java Bytecode is an important use case moving forward. It could have been when Rails/Django/Laravel were on top of the web framework game but the demand for this use case is diminishing.