Exchange Port 443

Accessing the account as an IMAP account, or using the Exchange Account preset to create the account on the iPhone which creates/enables the account via ActiveSync with the Exchange Server?

I'm no Exchange Server expert, but you can't change the port used/required by the account. This is determined by the Exchange admin at the Exchange Server.

Well, it would be very unusual to have Exchange running webmail and ActiveSync mobile device mail on any port other than 443. Port 443 is a default SSL port and almost all encrypted web servers use that or 8080 to communicate https traffic, including webmail and ActiveSync mail.

If you have an Exchange webmail access, with an address like:

https://webmail.example.com/exchange

Then it is using 443 and your iPhone should work. If webmail has an address that specifies a specific port number it will indicate that in the address like this:

https://webmail.example.com:8080/exchange (note the port number after .com)

And in that case I doubt you can make your iPhone work. Do other people in your company use windows mobile phones like the Moto Q or Samsung Blackjack and successfully access mail? If so they are using ActiveSync on port 443 just as your iPhone should.