There are a couple of things that cause phenolic flavors. One is stressed yeast. That can be from underpitching the yeast, or fermenting at a too-high or too-low temperature. Another cause can be infection, particularly if it's a "smoky phenolic" like your title says. The most common cause I've seen is in beers that use water that has chlorine or chloramine in the water supply. When that happens, chlorophenols are formed. This tastes medicinal, solventy, or "band-aid" flavored.