How close does a person have to be to another for the pheros to reach them? I.e., how many feet, or do you have to be on top of one another?
The closer the proximity the better. You need to be within four to six feet for optimal effectiveness.
You should read the sticky’s at the top of the men’s forum. You’ll find the answers to these FAQ there. 
Bella
A lot depends on air circulation. I figure conversational distance as a rule of thumb, arms length to double arms length. Hits get reported often at much greater distances though.