I'm getting a Morrison Phoenix 13" riser with extra long longbow limbs in a trade. I am interested in going to recurve limbs instead but I'm unsure what length I should go with so I don't experience finger pinch and still maintain a smooth draw cycle. My draw is 28"

Longer the better for smoothness. I draw 27.75 and prefer mediums over shorts on all the riser lengths I've tried.

As far as the length is concerned, I recommend buying the length that would result in a 60" bow.  How exactly the limb length will be designated, i.e. short, medium, long, etc., will vary from company to company, so you'll have to ask questions to figure this out.  You could probably get by with a 58" bow, but it will not be as smooth at a 28" draw as a 60" bow.

The second question, which you didn't ask, is how to order limbs that will give you the poundage you want with a 13" riser.  Generally, companies specify poundage for a particular riser length, and may provide a conversion to other riser lengths.  A rule of thumb would be to add a pound or so to the weight for every inch the riser is shorter than the specified length, but this is not exact.

According to the Morrison archery site the riser will add about 9lbs over a 25" riser.