What happens if I delete the app or change my phone?

Your Gourmet Passport account is linked to the email and password you used at the time of signing up. If you delete the app, then install it again, either on the same phone or on another phone, and log in with the same email id and password, then nothing changes and you continue using your account as you had left it. If you use Facebook login for the app on the new phone, that has same email as you used while creating your account, then also your app stays updated.