I’m changing to a new mobile phone, I’ve not ever login via my phone.. so do I need to do anything to refit my new device so the app works?

Thank you for sharing your concern in the Community page, atd. Let me share additional information about logging in to your account on your new device in the QuickBooks Online Mobile app.

To address the question, if you are changing to a new mobile phone and have never logged in via your phone, you will likely need to download the app on your new device and log in using your existing credentials. Most QuickBooks Mobile applications aren't registered to a particular device. However, you must have a specific user account. 

Therefore, you should be able to install the application on your new gadget and log in as you normally would. 

I'm also conveying a pair of valuable articles with additional information on performing with invoices in the QBO mobile app:

• Edit An Invoice Payment Using The QuickBooks Online App
• Track The Status Of Invoices In The QuickBooks Online Mobile App

Feel free to drop by again in the QuickBooks Community if you need further assistance finding or working invoices in the mobile application. We're always happy to help, atd.