- serafina -
According to LOA, if you have BOTH the desire of an Iphone and of helping economically your family, you should expect to be able to manifest money for BOTH.
In case you have to give a priority, the choice should be for the action that gives you most joy, which in your case was arguably the choice of sharing your money with your loved ones. I say arguably becuase that you were irritated all afternoon implies a certain inner conflict. Anyway, let's say that in your belief system an altruistic action creates joy enough for you to want to take that choice after all. Others with different belief systems would do otherwise, but here is you. Cool. Now even more so because you acted "good" (accumulation of merits as buddhists call it, or better said, belief in your heart that you're an even more meritevole person for acting like that - the universe doesn't really care as it is morally neutral, as LOA advocates)you should expect to be able to attract that Iphone very easily, if you still desire it. Wouldn't it be nice not to have to renunce to it after all?
Regarding careful spending, it also depends on what makes you happier. The comfort zone regarding money is very subjective. If you're a student and living on a student loan I suppose that either you attract another source of money or you keep
down with expenses. Either way is brilliant. Messing up and make debts would be hunting for troubles instead. But even debts can be solved with the LOA. So there are always second and third chances to be happy again, real messing up is practically impossible unless you really insist a big deal going upstream.