Whether or not to buy organic flour depends on what you are worried about. If you are just worried about pesticides and fertilizers (etc…) ending up in the flour, that is more of a concern for whole-wheat flour. If you are worried about the amount of synthetic chemicals that end up in the water and being inhaled by workers, both types are equally bad.
I am trained as a baker/ pastry chef and have worked in an organic bakery for some years in the past. Here’s what I understand:
ALL wheat “seeds” are treated with a fungicide (it is an organic one if it is organic flour). This is the law but it pertains to the “seeds” that actually get planted to grow the new wheat, not what gets ground up.
What I was taught about making bread is that it is VERY important to use organic whole-wheat flour because the synthetic chemical residue is much higher on whole-wheat flour. This is because only the wheat berry is left intact, unlike white flour where the outer layers are stripped away. Many people feel that the residue is significant enough to affect the process of making bread (i.e. affecting the yeast growth)
That being said, I use organic white flour as well because I feel it is important for so many reasons.
I hope this answers your question at least a bit!