Can be.
There are some strains that will pink up regardless of PH, and an actual Phosphorus deficiency is very rare.
But, generally, if you see red stems and petioles it indicates a low PH lockout.
Easy enough to check, yah?
I used to call it sunburn, because many plants tint their new growth red to reflect excess red and IR until they are old enough to handle it.
So far though, all of mine were PH issues.

Aloha,
Weeze