Above is a video from Google demonstrating how to setup IMAP email on the iPhone. The primary advantage of IMAP (Internet Message Access Protocol) over POP (Post Office Protocol) is that IMAP maintains the state of messages across email clients. For example, if you delete an email at Gmail.com, then that email is automatically deleted from your iPhone and vice versa. This means that you never have to deal with the same message twice and can save a lot of time when it comes to filing and deleting messages.
With IMAP, folders are also synced across email clients. When you switch to Gmail IMAP, the Gmail spam folder will appear on your iPhone. This allows you to flag messages as spam directly from your iPhone, something you couldn’t do previously with POP.
Follow the video above or these simple instructions to make the switch.