This link has lots of info on how to configure many clients - none specifically iPhone but certainly should tell you ports and configuration that should work.
The meat of this is:
* Email Address: firstname.lastname@example.org
* IMAP Server (Incoming): mail.example.net (port 143 has optional TLS encryption, or use port 993 with SSL encryption)
* SMTP Server (Outgoing): mail.example.net (port 587 has optional TLS encryption, or use port 465 for SSL encryption)
* User: email@example.com
(Note, if you prefer POP3 access, use port 110 for normal/TLS access, or port 995 for SSL access.)
Note that port 25 access is not necessary and SSL/TLS is available on specific ports.
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