A temporary stop on sending is what you had as a 453 error code. But if your iPhone email app is reporting that your mailbox sign in credentials (Username and password) are incorrect then that's a different error. Are you sure you entered the current password when setting up the app again?
Is your mailbox password strong enough? The mailbox authentication may have detected a weak password and declined to connect to your mailbox.
Hopefully you'll have pre-registered for password recovery an alternate email address and mobile number. Either can be selected in the password reset process to receive an emailed link or a 6 digit code by mobile text message to authenticate a password change. It's worth checking these Reset details are present and correct before opting to change the password assuming you can still sign in to webmail.
Select here: Sign in to TalkTalk Mail
Enter your email address and your email password, select Sign in.
Update your reset details is an option on the user avatar menu. Check, update and Save the Reset details if needed, then use the Reset password now button in the help page Changing your email password.
My recommendation is to exceed the minimum required and use a password of 12-15 multicase letters and numbers and a symbol. A new password created from multiple words gives an opportunity to memorise the password that, for security, needs to be unique to the mailbox.
