I’ve searched and haven’t found any info on this, can some one explain the best places to put pheros like instant shine?
That depends a bit on what effects you want…mainly self effect, effect on others, or both?
And also…the environment…If it’s cold and you have 10 layers of clothing on that changes things slightly as well 
These are my own perferred places…Assuming you are indoors;
- For mainly self effects: spray where you are likely to get most of the “phero fumes”…chest, front/sides of your neck
- For a mixed self & others effect: spray a bit on your chest, some on your wrists and some on the nack of you neck
- To mainly affect others: keep sprays to wrists and back of neck/hair
here’s a good start: Tisha's application tips
and then try xiphoid’s suggestions for what effects you want.
This may sound stupid but… when you say back/chest etc, do you mean on our actual body or over our layer of clothing?
On your skin 
Have a look at Tisha’s sticky about application tips in the ladies section…