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