To check what sort of mail protocol you are currently using on your iPhone device, please follow the below steps:

1. Open your iPhone settings page and locate the ACCOUNTS AND PASSWORD option and press to open.
2. Find the account you wish to check settings for and press to open the settings page.
3. On the settings page, you will see a reference to IMAP or POP towards the top, see the below image:
   
   
   
   You will see a reference to POP or IMAP, as shown above. POP account on the left, IMAP on the right.