Reaction of phenol with concentrated sulfuric acid What is the product when phenol reacts with conc. $\ce{H2SO4}$ in excess?

I have been told that the major product will be ortho at low temperature and para at high temperature. Why cannot it form both ortho- and para-substituted product as in the case of picric acid?
It's a reversible reaction, so at higher temperature the thermodynamic para product is formed from the kinetic ortho product.

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