When you get a new phone, even after migrating all your data and settings, XUMM accounts will not be automatically available in XUMM on your new phone.
For security reasons, XUMM does not store accounts / account secrets in your Google / Apple iCloud backups. If XUMM would store sensitive data like your account secrets in a Google / Apple iCloud backup, an attacker gaining access to your Google / Apple account(s) would be able to restore a backup of your device to their own device, resulting in the loss of your cryptocurrency funds.
This means restoring Xumm from backup will not work. The app needs to re-installed from the play store.
Accounts will then need to be imported using the credentials (seed/secret/mnemonic) on your new phone.
You must still have access to your existing account secrets: a family seed (s....), mnemonic (words) or 'Secret Numbers', the format XUMM generates.
So: even when moving all data of your phone or restoring a backup, you'll have to re-import your accounts with their secrets again using the procedure in this article.
This is why it's really important to keep your secrets stored offline in a secure place, but ready for use.
If you are using a Tangem account, you don't need your written down secret(s) (family seed (s....), mnemonic (words) or 'Secret Numbers') as you can just import your Tangem account by tapping your card against your phone in the account Import flow.