Check your IMAP settings in Gmail. If Gmail is not properly configured for the IMAP email protocol, you could receive connection errors when trying to load messages on your iPhone. To check your IMAP settings, open Gmail on a computer's web browser and log in.
• Click the Gear menu and select Settings.
• Click the "Forwarding and POP/IMAP" tab.
• Check the "Status:" filed in the "IMAP Access" section. It should say "IMAP is enabled". If it does not, click the "Enable IMAP" radio option.
• Click Save Changes if you made any changes.
If any other gmail issue then, Contact Gmail Customer Service help desk or you can visit here http://www.avtechnumbers.com/gmail-customer-service.php