Create a new account

Open iPhone Settings application and choose Mail, Contacts, Calendar:

Then select Add Account...:

DavMail is not an Exchange ActiveSync server, press Other:

Choose Add CalDAV Account:

Enter your DavMail server hostname in the Server field, append ':' and port if DavMail HTTP (Caldav and Carddav) port is not 80, provide your username and password then press Next:

On the account page, open Advanced Settings:

Enable SSL and check port, make sure Account URL is https://davmailhost:1080/principals/users/username@company.com: