Ok there are no good specs for the Phase II or the master feeds.
What have you been feeding her in the past?
You want to reduce caloric intake to slow her rate of growth while not reducing the other nutrients which are critical for proper bone development. You must continue to meet the her requirement for protein, minerals and vitamins.
One of the ways in which this can be nicely done is by utilizing a protein, vitamin, mineral supplement such as Born to Win by Purina which supplies all of the protein, vitamins, and minerals she needs in her diet in a very concentrated formula and without all that extra calories and energy that she does not need. Yes it will contain 32% protein and yes everyone freaks over this. Think of it as orange juice concentrate in a can versus a gallon of ready to drink oranje juice. They both have the same nutritional benefits but you'd have to drink a lot more of the ready to drink as opposed to drinking the concentrate straight out of the can. (Ok so that's not a GREAT example but hopefully it will help, lol).
On the Born to Win for a yearling estimate her weight (http://www.gaitedhorses.net/Articles/horseweight.html) then multiply that by 0.0018 to get the actual amount to feed for her weight. Say if she's 750lbs that's 1.35lbs per day. Since she is having a problem with physitis I would add 1/2lb to that for 60 days to get her straightened out. Measure the circumference her affected joint(s) and do so weekly or bi-weekly to keep track of how she is doing and also make note of any heat or lameness.
===================== Keiki & Summer =====================<!--color-->
Click to visit Huck's website