No, changing the phone/number would not resolve the issue. Your iPhone knows you have two AppleIDs. You probably have music, apps, or movies from two different AppleIDs on your device. You can go ahead and change over to the new one, but if you need to download old music, apps or movies from the previous AppleID, you won't be able to. This is done intentionally to prevent people from creating multiple IDs for multiple free trials.