iphone doesn't connect

This is a guess as there aren't any details in your question:

iPhone will not pair via Bluetooth to a computer (Mac or Windows) except for personal hotspot and then only if your cellular plan supports it.https://discussions.apple.com/docs/DOC-7722

If you are attempting to use Handoff/Continuity, that does involve Bluetooth but the devices are NOT paired; Bluetooth just needs to be on and the devices in range of each other. The following may help with Handoff/Continuity issues: http://support.apple.com/kb/TS5458

You probably have to connect your iPhone to your MacBook Air using the lightning connector instead of bluetooth

It could be that your port on the bottom of your phone has got lots of fluff in it (I had this problem myself and with it charging). A handy tool to use is the sim ejector that came with the phone, use that the clear out the fluff and it should connect easily.

(this will help if it is a lightning cable you are connecting with).