First take your iPhone and login to your cPanel account from your Safari browser.
The URL you should use is yourdomain.com/cpanel where you should replace yourdomain.com with your actual domain name. This would take you to the cPanel login page where you should enter your login details.
If you are not sure what your cPanel login details are, you can easily locate the username from your User Area-> My Accounts-> Information and settings-> cPanel username. You can change the password from there as well.
Now you need to locate the Mail section and click on Mail Autoconfig.
You will be redirected to a new page with the supported email clients. Click on the Mac Mail button.
After that choose the domain name your email account is using and the email account itself as well and click Submit.
Once you click Submit you will need to click on the last Link next to iOS for iPhone/iPad/iPod and MacOS® Mail.app® for Mountain Lion (10.8+)
After that you will see a message stating This website is trying to open Settings to show you a configuration profile. Do you want to allow this?. Click on the Allow button.
You will be redirected to the Install Profile page where you should just press the Install button in the top right corner.
Next you will be prompted to enter your iPhone's passcode (if you have such).
On the next step again click on the Install button.
Afterwards you should enter the email account’s password. When ready - press the Next button.
The final step would be to click on the Done button and that's it!
Now you can open the MacMail App on your iPhone and you will see the email account setup there and ready for use!