Your son's insecurity is being preyed upon
Getting the iPhone isn't a solution. Building up your son's confidence and capability will arm him against bullies and internal insecurities.
To build these up I did martial arts as a teen and it helped me a lot.
Caving to peer pressure is not a position of strength.
On the other hand it can also be the case your son wants an iPhone. In this case good to chat with him.