Your data is saved with Between ID on the cloud. If you change your device, you only have to reinstall Between and log in with your ID/password to continue where you left off. You don't have to use Disconnect-Reconnect.
If your phone number has changed, you can update it on your partner's app. Tap open your profile and press Edit to update your phone number. Likewise, you can change your partner's phone number on your Between app.
*Please make a note of your ID/password before changing your device.