How to change the Apple ID on my iPhone?

Again, it sounds like you didn't change your address properly but instead created a new account.

Here's how you change the email address (Apple ID) you use for your Apple Account while retaining everything in your account:

If you have an iPhone or iPad:

1. Go to Settings, then tap your name.

2. Tap Sign In & Security.

3. Next to Email & Phone Numbers, tap Edit.

4. Tap the Remove button next to the email address, then tap Delete.

5. Tap Choose Another Email Address and enter your device passcode if asked.

6. Enter the new email address, then tap Continue.

7. Enter the verification code that was sent to your new email address. Read this support article to learn what to do if you didn’t get the email —> If you didn't receive your verification or reset email - Apple Support

8. If you encounter issues with certain services after doing this, this outdated support article may still have useful suggestions --> What to do after you change your Apple ID or password - Apple Support

Refer to the support article Change your Apple ID - Apple Support :

- If you don’t have an iPhone or iPad the support article says to, “go to https://appleid.apple.com and sign in. Then follow the onscreen instructions to change the email address associated with your Apple ID.”

- For general information, and other issues such as changes or addresses not being accepted.

- Note a recent change to the article where you can now change the email address without having to have access to your old email account.

How to change your Apple ID email address online:

1. Go to https://appleid.apple.com and sign in.

2. In the Sign-In and Security section, choose Apple ID.

3. Enter the email address that you want to use as your Apple ID.

4. Choose Change Apple ID.

5. If you changed your Apple ID to a third-party email address, check your old ID email for a verification code, then enter the code. Learn what to do if you didn't get the email. --> If you didn't receive your verification or reset email - Apple Support

6. If you use services like iCloud or Messages to share with friends and colleagues, sign in to those services with your updated Apple ID, as indicated in this support article —> What to do after you change your Apple ID or password - Apple Support

If you have created a separate ID then the best thing to do is go back to using your old one. If you need it I can post instructions about performing a partial merging of the accounts but this is cumbersome and not 100% effective. You are better off changing your email address on the old account but Apple will not let you use the email address that you used for the newly created ID. You will need yet another email address.

To me it sounds like you have a different account on that phone, otherwise when you change the email address on one device signed into an account it changes it on all the others too.