When looking at a list of emails, the iPhone can display the first few lines of the email, up to five, or none at all to make a more compact list. It’s easy to change this preview length to find what works best for you.
To change the size of your email previews, tap the Settings icon on the home screen and tap the Mail button.
Under the Messages section of Mail options, tap where it says Preview. A list will slide in with options from None to 5 Lines. To see how it looks, press the Home button (below the screen) and then tap the Mail icon at the bottom of the screen to quickly access your email.
With None selected, you will see only the Sender of the email (in bold) and the first part of the subject line. Adding more lines to the preview will show more of your email’s content at the expense of showing fewer emails on the screen.