Potential Bug: `.PHONY` targets and order-only prerequisites

[Jacob Kopczynski]

I'm unsure whether this is a bug or just undocumented, but I found a confusing interaction in a simple Makefile:

.PHONY: up
up: down | down-clean
    docker-compose up -d
.PHONY: up-clean
up-clean: down-clean up
.PHONY: down
down:
    docker-compose down
.PHONY: down-clean
down-clean: 

    @echo "running down-clean" 

    docker-compose down -v

The interesting parts are up: down | down-clean and up-clean: down-clean up. Docs state this is how an order-only constraint should be imposed.
My goal here is to ensure order - when running up-clean, down-clean must be run before up. But if I'm just building up, down-clean should not be built.
However, with both GNU make 3.81 (system, Mac OSX) and GNU make 4.3 (latest, gmake installed from Homebrew), I see this treated like a normal prerequisite:

$ make up
docker-compose down
<...>

running down-clean

docker-compose down -v

Removing volume <...>

This is not the expected behavior. Is this an expected interaction with .PHONY?

Thanks,

Jacob Kopczynski