concolor likes it fairly bright. not nearly catt levels, but definitely higher than a phal.
some paphs can take a while to develop their buds...I don't recall concolor being one of them, but you never know.
and of course you have other issues, like temperature changes (cooler temps will slow down bud development but will not adversely impact blooming as long as the temps are within the range for the plant), underwatering, overwatering (leading to root rot), humidity issues, and sometimes paphs just blast their buds in response to an environmental change (although this happens much much much less frequently than with, say, phals).
but based on what you're telling us, I'd move it to slightly higher light. and remember that brachys like pure water low in salts (resist the urge to fertilize), and they really hate soggy medium. as long as the water is pure, you can let them dry out a bit between waterings.