Can I run the app on two mobile phones? I've installed it on another phone as I think my current phone is about to die, but I cannot log on with my credentials.

I can provide you with some insights about how QuickBooks Online operates, dogdayscornwall.

Please know that the mobile app is designed to be used by a single user at a time. Therefore, it's unable to run simultaneously on two smartphones. 

If you try to access the same account, the first device will be logged out automatically. You'll also be prompted to re-authenticate on the second one. As an alternative solution, we can use a mobile browser to be able to work concurrently.

When moving to a new phone, make sure to enter the credentials you used to set up your company. Additionally, it's recommended to properly sign out from your old device. This will ensure a smooth transition and prevent any login issues.

To learn which functionalities are supported on iOS and Android, check out this article: Compare mobile app features.

I'm just a comment away if you need more help in managing books, transactions, and reports. Feel free to tag my name below. Have a great rest of the day!