Here is my take on phenolic flavors and how to control or "dial" them in (or out). First, phenolic flavors can be described as burnt rubber, spicy, licorice, peppery. This is a characteristic flavor in german Wiese beer and some belgians. These flavors should be very subtle if they are appropriate for the style at all.
In my experience the level of phenolic flavor (and other flavors) is a function of the fermentation temperature, wort aeration (or oxygenation), the health of the yeast and the pitching rate. There are other factors as well, but these are the ones that I have been playing with. I have found that there is strong interaction between these variables, but to varying degrees. For example, you could adjust the fermentation temperature to change the level of phenolics, but I have found that that effects other flavors such as esters more than it effects phenolics. The thing that I have found to effect phenolics the most is the pitching rate. Keeping all other factors equal, increasing the pitching rate reduces the phenolics (to a point). In general, using the standard pitching rate as computed by the pitching rate calculator on mrmalty.com produces reasonable levels of phenolics depending on the yeast, etc. If you under pitch, you could end up with high levels of phenolics. I struggled with this problem a belgian blonde ale that I made about a dozen times before I realized that I was under pitching. The phenolics were so strong that it was almost undrinkable. Once I started using the pitching rate calculator, the phenolics went way, way down! The slight bannana ester flavor did not change much. If I want to get a little more phenolics, I can pitch slightly less yeast (say 10% less) and get slightly more phenolics without changing the fruity esters very much. Holding the aeration and pitching rate constant, I change the fermentation temperature to adjust the esters without changing the phenolics very much. This is just what I have observed on my system. Your mileage may vary. I am now working on dialing in my wort aeration using pure 02, but that is another story. If anyone else has had similar or different experiences with this I would like to hear them.