I accidentally clicked on a Facebook virus while on my iPhone. Can the hacker access other apps on my phone?

There is no known malware capable of infecting an iPhone, unless it has been jailbroken (ie, hacked to allow apps from outside the App Store). So, whatever it was that you tapped, it didn't infect your iPhone, assuming you haven't jailbroken it.

If that Facebook virus took over your account and started posting spam etc. here's how to get rid of it

http://facecrooks.com/Internet-Safety-Privacy/how-to-protect-your-facebook-accou nt-from-rogue-applications-292.html/