You can use Phalcon+ to integrate with RR. Phalcon+ provides PSR-7 converter-classes:
PhalconPlus\Http\NonPsrRequest to help converting PSR7 Request to Phalcon Native Request,PhalconPlus\Http\PsrResponseFactory to help create PSR7 Response from Phalcon Native Response.and other finalizer to process stateful service in di container.
Phalcon 4 has builtin supports for PSR-7:
you can easily integrate with RR.