There are other causes of extremely dry skin...flaking.

1) low intake of Essential fatty acids is one common cause.

This would be flax oil and fish oil. You could start orally at 1 gram of flax and 3 grams of fish oil to start. (you can also use Krill oil, instead of fish oil...it is more potent so 2 of them a day should be enough.)

2)If your circulation to the feet is impaired then nutrients cannot get down there. If you soak in epsom salts daily, the skin will soften and the dryness will improve. Magnesium may not get to your feet for the same reason I gave above. People who take baths tend to have softer skin than people who shower. Soaking in a tub tends to hydrate the skin much better. You can also put epsom salts in the bath tub...but be careful getting out, as it can be slippery.
6-8 oz in of salts in a bathtub of lukewarm water is often sufficient. Soak at least 1/2 hr or so.

3) you could try high dose Biotin, 5 or 10mg a day to improve skin tone.

4) There are magnesium lotions and creams you can put on your feet. Epsom-It and Kirkman magnesium cream are two good ones. Available on the net easily.