From what I've tried to understand, Aristotle believed that practical wisdom (phronesis) is an intellectual virtue. And also, virtues are found at the mean between excess and deficiency. It seems to me that therefore phronesis must be a mean between two extremes: however, I'm unsure as to what those extremes could even be. Does Aristotle restrict his mean analysis on some virtues, or does he mention, or could there be, plausible extremes for this virtue?
In Aristotle's psychology, man has a soul with three tiers of sorts: the vegetative (pertaining to life functions), the animal (pertaining to locomotion and the senses), and intellectual (dianoia and noesis). What later philosophers like Plotinus called the "civic virtues," like courage, are indeed a mean between the extremes of excess and deficiency. Both lead to injury of oneself and their community. This is largely in part because animal functions, being a mix of form and matter, can suffer from deprivation or excess. Consider a few examples: too little food and one suffers from being hungry, too much food and one suffers from being full; one cannot see from a deficit of light, one feels intense pain if one encounters too much light (i.e., both are blinding). It's basic Aristotelian biology that the civic virtues will always be a mean between extremes.
The intellectual virtues are different, in virtue of the purely immaterial nature of that aspect of man's soul. Does one feel pain at understanding too much? Is too much wisdom injurious? Aristotle didn't think so. The intellectual component of man's soul is free to receive essences without impurities, and contemplate them as such. Excess is virtuous in this regard.
Long answer, but in short: no, the intellectual virtues (like phronesis) are not a mean for Aristotle. These are rare in their property that pursuit of them to excess will not be injurious. In fact, it is good to pursue them without limit (in combination with the other virtues, of course).