The Physician is a good doctor- if you judge him only on the amount of money he makes and not by his actual skill. He knows the cause of every patient's illness and the perfect drug to cure it because he has a deal with the pharmacists to share in the profits.
The cause being known, down to the deepest root,
Anon he gave to the sick man his boot.
Ready he was, with his apothecaries,
To send him drugs and all electuaries;
The narrator describes him as wearing
In blue and scarlet he went clad, withal,
Lined with a taffeta and with sendal;
And yet he was right careful of expense;
He kept the gold he gained from pestilence.
For gold in physic is a fine cordial,(25)
And therefore loved he gold exceeding all.
This tells us that the Physician is wearing expensive silk (sendal) lined taffeta (think 80's prom dresses). Like our other wealthy pilgrims, his dress shows color and expense. We learn that he makes his money not just from aiding the ill and sick, but from collecting gold as though it were a "fine cordial" (or tonic- liquid medicine).
Despite all his studying, Chaucer makes sure to point out that our gold loving physician has not studied the Bible, and works to cast a doubt on his skills as an honest doctor.