what if i dont want the folder structure on the server.
Then don't, but the only way to create additional mailboxes for access with the iPhone's mail client is with an IMAP account by creating additional server stored mailboxes for the account.
An IMAP is designed to have all server stored mailboxes for the account identical with each email client used to access the account with each server stored mailbox kept synchronized with the server automatically with each email client used to access the account.
Email account mailboxes and messages are not included with your iPhone's backup, so if you restore your iPhone with iTunes if needed or wanted, all locally stored mailboxes for an account will be lost in the process. And with a POP account, received messages no longer available at the incoming mail server for the account will also be lost, and when the account is recreated, all received messages that remain at the incoming mail server will be downloaded as new and unread messages again.
Not the same with an IMAP account. All server stored mailboxes and messages within will be restored with the account is recreated and all received messages already read and marked as such will be marked as read when the account's Inbox mailbox is re-synchronized with the server.
Although a POP account can be accessed with more than one email client, a POP account is designed to be accessed with a single email client only. An IMAP account is designed to be accessed with more than one email client with all server stored mailboxes kept synchronized with the server automatically with each email client used to access the account. This came about when laptops became popular - using a Desktop at the office and a laptop when traveling or when out of the office. Send a message with the email client used on the laptop and the sent message will be available in the account's Sent mailbox with the email client used on the Desktop automatically, and vice-versa. The same applies with the iPhone's mail client, but to each his/her own.
At the current time, it isn't possible to create additional mailboxes with the iPhone's mail client with no way of knowing if Apple has any plans to incorporate this with a future firmware update.