Although the milk secretion of calcium and phosphorus is independently regulated, the median ratio of calcium to phosphorus is 1.7 in both preterm and term breast milk. Like calcium, the concentrations of phosphorus are highest in early transitional milk and decrease gradually as lactation progresses.

Reference:

Dror DK, Allen LH. Overview of nutrients in human milk. Advances in nutrition. 2018 May 1;9:278S-94S.

Dorea JG. Calcium and phosphorus in human milk. Nutrition Research. 1999 May 1;19(5):709-39.