Just sign out of the ID on one of your phones, then sign into the other ID.
Read this document to learn how to sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or Mac --> Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or Mac - Apple Support
For an Apple mobile device:
1. Go to Settings, then tap your name.
2. Scroll down to the bottom.
3. Tap Sign Out.
4. Enter your Apple ID password and tap Turn Off. (Read this if you If you forgot your Apple ID password - Apple Support )
5. Turn on the data that you want to keep a copy of on your device.
6. Tap Sign Out.
7. Tap Sign Out again to confirm that you want to sign out of iCloud.
Read this support article to learn how to sign in with your Apple ID on different devices--> Sign in with your Apple ID - Apple Support
For an Apple Mobile device:
1. Open the Settings app.
2. Tap Sign in to your [device].
3. Enter your Apple ID and password.
4. If prompted, enter the six-digit verification code sent to your trusted device or phone number and complete sign in.
If you do not erase the second phone before signing into the new account you will be given an opportunity to keep the old data too, or delete it. You can always delete it later if you wish. However, since these two IDs will be set to different countries you waon't be able to share items with Family Sharing so this may be a one time opportunity to easily retain content from the old ID on that device.