Hello Darren Corbett,
Good morning!
Thank you for publishing in Microsoft Community. We are happy to help you.
Based on the description you have shared; the issue can be related to our SPO team; however we need to confirm some information with you before we move to the dedicated team1-Make sure that you are signed in to your Microsoft account on your phone. You can do this by opening any Microsoft app and checking if you are signed in.( the same account as your computer apps)
2-Some qualifying plans have a screen size limit of 10.9 inches for editing in the Microsoft 365 mobile apps. And all non-qualifying plans have a screen size limit of 10.1 inches. For example, if you're using an iPad Pro with a 12.9 inch screen, you must have a qualifying Microsoft 365 plan with access to the desktop apps to edit files.
Check below to see what features are available with your plan or version of Office. See What Microsoft 365 product or license do I have? if you're not sure what plan you have.
Reference: What you can do in the Microsoft 365 apps on mobile devices with a Microsoft 365 subscription - Microsoft Support
3-Check if there are any updates available for your phone's operating system and the Microsoft apps. Updating to the latest version can help resolve any compatibility issues.
We look forward to your reply. This requested information will help us narrow down the scenario and find if we need to move to the dedicated team or not. We will continue to assist you based on the information you provide. I sincerely appreciate your patience and cooperation.SincerelyEben Ezer Tres | Microsoft Community Moderator