Greetings AppleUser756,
We see that you're having a problem with your mail not syncing properly from your iPhone to your other devices, and we understand how this can create confusion. You've come to the right place for assistance with this.
When you set up your account with your iPhone, did you manually set it up or did you select your email provider in the list? If you set this up manually, let's see if you selected IMAP or POP preferences. You'll want to make sure that you selected to use IMAP. For more information on this and how to set up the email account again if you need, check out the following resource:
Add an email account to your iPhone, iPad, or iPod touch
If you see that correcting settings or adding your account again doesn't resolve this, do you see that this is occurring with multiple email accounts or have you only noticed this with one account on your iPhone?
We look forward to hearing back from you.
Cheers!