If the phone landed on your mac at the top of the keyboard near the display it may have damaged the cable
from the logicboard to the display. This could simply need reconnecting or replacing, at worst it could be the
graphics card in the mac, these cannot be replaced and a new mac may need to be considered.
The best thing to do is make a Genius appointment at your local Apple Retail Store if you have one and it is open,
they will assess the mac and give you an indication of what might be wrong and what can be done to remedy it.
If you do not have an Apple Retail Store open or near you then you may have to take it to an Apple Approved
Service Centre, and make sure it actually is Apple approved, and not just saying it is. You will also need to make sure
that they are not going to charge you for looking at it, and if they offer to repair it for you make sure that the price they
quote is the absolute final price. Too many people get a quote and when receiving the mac back they get a higher bill as
the repair person found 'other items that needed fixing/ replacing etc etc'.
How old is this mac, is it under warranty, do you have Apple Care, is it covered for accidental damage.
Get hold of your brothers bank account, then get yourself a new brother.