calcium and phosphorus have an inverse relationship
that's why people with ESRD have to limit phosphorus intake cause it can cause calcification of blood vessels etc...they have altered acid/base balance
phosphate excretion is diminished in Renal failure leading to hypo-calcemia which also contributes to bone loss (pathological Fx's) as does the diminished synthesis of Vit D inherent in renal failure.
with that said, a normal healthy individual have internal controls (buffers etc) which help to maintain a good acid/base balance.