Fluoroantimonic acid - $\ce{HSbF6}$ is made by combining $\ce{HF}$ and $\ce{SbF5}$. In this system, $\ce{HF}$ releases its proton ($\ce{H+}$) concomitant with the binding of $\ce{F-}$ by antimony pentafluoride, which is a Lewis acid. The resulting anion ($\ce{SbF6-}$) is both a weak nucleophile and an extraordinarily weak base.
Two things to note are:
- $\ce{HSbF6}$ is a very strong acid.
- Its conjugate base is a very poor nucleophile.
The hydroxyl group of phenol attacks $\ce{H+}$ and makes phenylhydronium ion which would behave like a nitro group. Therefore, the substitution would occur preferably on the 3 position.
Since $\ce{HSbF6}$ is such a strong acid, you can safely assume that virtually all of the phenol is protonated all the time.