Either one, but you need to think about the "mechanics" of the uptake. In other words, "yes", it can be applied as a foliar spray, but does the plant respond well to that?
Many orchids are notoriously poor at foliar uptake, because they have waxy cuticle layers on the leaves, which evolved as part of the plants' water retention strategy. Unfortunately, a coating that prevents water loss is probably pretty good at preventing uptake as well. Phalaenopsis have very thick layers, so are poor at foliar uptake, and in my opinion - based upon observation only - paphs are up there, as well.
Generally, young plants have not yet had time to develop the waxy cutex to a significant degree, so are better about foliar uptake than are mature plants, and plants with thinner leaves tend to be better at it than those with thicker leaves. For example, I speculate that "strap-leaved" paphs are better at it than mottled-leaved ones, and that phrags are even better.
Again - and this seems to be the only "universal" thing I can think of about orchid culture - it's not an "all or nothing" scenario. Plants that are poor at foliar uptake still do some... Besides, if you spray a plant thoroughly, much of it drips into the substrate anyway, giving the plant the opportunity to use its roots.
