So there must be some range of environments in which an organism (via genes) is able to produce the same phenotype regardless of where its environment falls within that range.
The organism needs to successfully thrive and reproduce within that range. Sometimes this means tailoring its phenotype to the environment it finds itself in.
Of course.
But imagine a world in which environment truly was more determining than genes. Every animal born in a swamp would be a frog (no matter what its parents were) and every animal born in a tree would be a bird. Perhaps coloration or some other trait might be heritable — blue birds who move to swamps give rise to little blue tadpoles — but the majority of phenotypic features would be governed by the environment in which the organism is born and develops.
In our world, all we know about X is that it is a phenotypic feature, then we should expect it is ...
Here's the new thread for posting quotes, with the usual rules: