According to my understanding of what a phenomenon and concept are, I believe that uniformity is both, a phenomenon and a concept, it is a phenomenon since it is evident in nature (numerological invariance in petal, seeds, leaves of plant species) but also a concept since it is also established sub consciously, (created uniformity), as in the interpretation of what is beautiful. I believe that since the perception of beauty is extrinsic instead of it being intrinsic, the uniformity of what is beautiful would be a conceptual element of our studies. Even though people tend to generalise beauty, beauty is indeed in the eye of the beholder. What do you think?
It is a concept, more properly a baseless assumption held up by confirmation bias alone.
As Quine points out in discussing Natural Kinds, were it a phenomenon, it could not be observed without assuming it. You cannot observe a consistency without comparing two things that are not identical and declaring them to be the same.
Two things are objectively never identical, or they would not be two things, and the difference could always be significant in any case, if we did not harbor the bias that most distinctions are not going to be significant.
Of course that bias is what allows us to sort through differences and learn categorizations. But it is not a fact, it is an assumption. Even if Kant is right in making it the basic content of a Category, meaning that it is necessarily shared by all thinking beings, we do not see the truth, we only see what aspects of reality are compatible with thought.
Conifold's comment stimulates this idea, which in fairness he might not share. There are two issues here.
Suppose you see a zebra. It is a phenomenon, something perceived or sensed. Now, you cannot perceive or sense anything without applying some concept or set of concepts to it. You might think you have seen a striped horse, a striped animal, a quadruped, a creature with hooves, something that canters or gallops. You cannot perceive (or think you perceive) anything without bringing it under some description : and descriptions are conceptual. If you see the zebra as a horse, you have used the concept, horse.
This, I should say, is a human universal : no perception of phenomena without concepts. But the concepts we apply are usually and almost certainly, and possibly universally, culturally specific. A particular culture may not have the concept, hoof : it may regard what I call a hoof as a horn-like decoration or the zebra as a unicorn mysteriously missing its horn. These examples are light-weight but they illustrate the important point that different cultures or language groups can 'see the same thing' - what a photograph might represent - but apply quite different concepts to it and in this sense 'not see the same thing'.
There is no paradox here. We just need to draw distinctions. Interesting question, btw.