PICA can be a caused by a primary Phosphorus deficiency, but currently a more likely cause could be a lack of dietary fibre, so providing access to straw/haylage in the paddock, raceway or close to the parlour will be an option if you can get them to take it!
A secondary phosphorus deficiency can also be caused by the increased sugars present in the high quality grass that cows are currently consuming, so supplementing with a free access mineral lick, low in molasses not only provides supplementary phosphorus but many other minerals, trace elements and vitamins