Hi Merlin Schwartz,
Welcome to Microsoft Community.
The answer is that in the Excel for mobile application, you cannot access Named Ranges. This has been clearly stated in the help article: Define and use names in formulas - Microsoft Support
I have also tested this with my Excel for iOS app, and as described in the help article, accessing Named Ranges is not possible.
I would like to add: Excel Online does support Named Ranges. You just need to access Excel Online through your mobile browser to achieve "accessing Named Ranges on your phone."
I hope my explanation has clarified your doubts. If you have any other questions or want to share more context, please let me know in your reply!
Best Regards,
Thomas C - MSFT | Microsoft Community Support Specialist