Though its name says acid, it's not really an exfoliant. It's a plant extract with some antioxidant properties. Its main thing in cosmetic products is to neutralize the metal ions in the formula (that usually get into there from water) that would otherwise cause some not so nice changes. It's a natural alternative to sometimes bad-mouthed chelating agents, EDTAs.
Show me some proof
- Khemis, Abdallah, et al. "A randomized controlled study to evaluate the depigmenting activity of l‐ascorbic acid plus phytic acid–serum vs. placebo on solar lentigines." Journal of cosmetic dermatology 10.4 (2011): 266-272.
- Sarkar, Rashmi, et al. "Comparative evaluation of efficacy and tolerability of glycolic acid, salicylic mandelic acid, and phytic acid combination peels in melasma." Dermatologic Surgery 42.3 (2016): 384-391.