cPanel Knowledge Base: How to Set Up a cPanel Email Account for iOS and Android
Email account setup on iPhone
https://www.namecheap.com/support/knowledgebase/article.aspx/1334/2186/email-account-setup-on-iphone
https://www.namecheap.com/support/knowledgebase/article.aspx/1334/2186/email-account-setup-on-iphone