You either moved the icon to another space on the iPhone, so you can flick to see if that fixed it- Or go to "Settings, General, Restrictions" and see if that's turned on... If it is, make sure "Safari" is enabled.
Your iTunes should actually have a backup so when you re-sync it should add the software back to the phone... But if those don't work and you did Hijack the iPhone you may to have to try some Google searches or go back to those forums for extra details.
Like One Orange Tree said, if you do that with the phone while it's Jail-broken then you may actually brick the phone rendering it useless.