First, make sure on the settings on your iphone are correct. From the main screen on your iPhone calendar, touch the upper left <Calendars> button. Make sure "All iCloud" is check marked (to the right of the "all iCloud" text. If it is not, touch it to activate the check mark. Touch <done> in the upper right hand corner. That may help.
If it does not, go to <settings> app on your iPhone. Make sure the "Account" field has the same name and login information that you are using on your macbook. Touch the "account" field, and type your password into the <password> field. Touch <done> in the upper right corner of the screen.
Make sure "Calendar" is turned on with the slide "on/off" button, and "contacts", "reminders", while you are at it. Touch settings to return. Hopefully iCloud is now working.
If not, go back into <settings> <iCloud>, and turn <iCloud> off and then back on.