The pattern calls for a cast on which is going to bump out the top part of the foot. Later, a bind off is called for, again one stitch at the beginning of the next two rows. That’s not the more gradual slope that an increase and later decrease would give but a step out and later a step in to shape the foot.
As far as keeping in ribbing, you won’t be able to continue with k1, p1. If you increase as given you’ll now be doing p1, k1 across the row and ending with a p1. Another way to do this is to look at your sts. If you see a V as the next stitch on the left needle, knit it. If you see a bump or a stitch with a little collar around it, purl it. That’s sure to keep your ribbing pattern intact, even with the extra sts.