Why dont my address book contacts from my mac sync to my phone?

I am trying to sync all of the contacts in the address book on my mac to my iphone.. I plugged in my phone to itunes and clicked sync address book contacts and on the bar at the top when it was syncing it said "syncing contacts" and everything but when i unplugged my phone the contacts werent there, however the few contacts i do have on my phone were added to my address book on my mac... so does anybody know why my contacts are transferring from my phone to computer but i cant get the contacts on my computer to be on my phone??