Even if you change phones, you can continue to use FamilyAlbum Premium as long as you do not cancel your subscription.
Just log in to your account on your new device and you'll be able to continue viewing your albums.
*You must register an email address to log in. If you haven't registered an email address yet, please register by starting the app, going to the Settings tab, and tapping Email under Login Settings.
*Payments will continue to be made from the previously registered App Store / Google Play account.