I dont think so. The phytochemicals will be liable to degradation into nutrients and the plant needs good specific conditions to manufacture its own phytochemicals, so that will depend on other conditions the plant is exposed to.
Foliar feeding is a technique of feeding plants by applying liquid fertilizer directly to their leaves. Plants are able to absorb essential elements through their leaves. The absorption takes place through their stomata and also through their epidermis. Transport is usually faster through the stomata, but total absorption may be as great through the epidermis. Plants are also able to absorb nutrients through their bark.
hormones have also been given, so phenols can be experimented
I agree, perhaps it can be a good research question that can be observed with time. Not necessarily expecting an increase in the same phytochemicals but just to see if there will be any difference from a negative control.
we have observed increase in phenolics during some biochemical reaction chanins by changing in micronutrients composition , so I think there might be an increase in phenolic contents but will the compounds remain (stable) or decompose later have to be tested.