The green colour in phlegm and snot is the result of a protein made by the immune system to fight infection, and by no means it should be the reason for the antibiotics prescription. Pharyngitis, sinusitis, and viral infections also, in most of th cases, do not require antibiotics.
A recent German cross-sectional study including otherwise healthy patients from a general practice with an onset of acute cough analyzed the phleghm of 241 patient complaining about the cough. The bacterial infection was confirmed only in 28 cases (just 12%); these results demonstrate that the colour of the phleghm and snot can not be considered a valid evidence when distinguishing between bacterial and viral infections, and therefore shouldn't be seen as a reason to prescribe antibiotics.
Unreasonabe use of antiobiotics is dangerous in many ways. First, and the scientist keep warning the patients about this, it boosts the antibiotic resistence in bacterias, which means soon the antibiotics we are used to may not be working anymore. Second, the antibiotics have a lot of side effects, so their use should be clinically justified. The other important fact is frequently ignored: antiobiotics also destroy the good bacterias, which are essential for our body. The lack of such bacterias may lead to dysbiosis, diarrhea and candidiasis. Antibiotics may also cause a strong allergic reaction, and even Anaphylaxis. So, why would you risk when there is no need to?
Also see: “Antibiotics and you” (14.11.2012) Health Protection Agency