How can i use my iPhone to scan a barcode and send it to my EV3 brick?
You will have to write an application for your phone that can scan the codes and then send the information to the EV3 via bluetooth or wifi.

If you don't know how to write iOS apps, start here.

For scanning bar codes there seems to be good info here. It appears that bar code scanning is built into iOS 7. If you have an older version, the the zxing library sounds like a good choice.

For communicating to the EV3 over bluetooth, this has been asked before. However, I have yet to come across a good example.

You should be able to figure out the communication protocol for communicating with the EV3 from the LEGO firmware documentation, VM documentation and source code.