FYI....I just submitted my first application! Whoo hoo! Here is the email I received from PhORCAS, they explain it much better than the FAQ section on the website:
PhORCAS would like to remind you of the benefit of submitting your application early. Submitting your application before your designated programs deadline dates will ensure a smooth application process. Programs will have access to view your application and begin reviewing it before transcripts and references have submitted. Any transcripts or references received after you submit your application will be updated to your designated programs. Please keep in mind with holidays coming up, registrar offices may be closing. Put in requests for your transcripts before the holiday break.
Also, it is important to know that you do not need to submit your applications to all of your designated programs at once. After you submit your application, you will still be able to log in, upload documents, and designate new programs.
I went back into PhORCAS to make sure after I submitted and it appears you can still upload and change a few things. However, you cannot change things under the "extracurricular" etc. But you can still upload letters of intent, add a newer version of your CV and such.
Hope this helps!