One option is indeed a browser-based interface, which is quite doable with an AI assistant even if you have little to no experience.
Another is to use Microsoft PowerApps to create the mobile interface. One advantage is that the same app runs on virtually any device, even the Windows desktop.
I assume the reason they want the mobile interface is so that they can use the application while away from their desktop computers. Otherwise, there's no advantage to it. The real estate available on even a large format smart phone is severely limited when compared to even a laptop. I've developed enough PowerApps apps to know how painful it can be to create a usable interface for that format unless you're willing to slim down the features considerably.
And that brings up another aspect of the decision. What, specifically, do people need or want the smart device interface to do? Is it ALL of the functionality of your Access app? Or are there elements of the app that can be usefully supported for mobile use? Data input, for example. How about reports? Do they need to be on a phone? Can your basic reports even be created so that they are usable?
I suspect that sometimes people want their apps on their phone just because they want to have them there, not for any practical reason. If your users do have practical arguments for a mobile interface, fine. That's not hard at all. But do take the time to sort out the whys and the whats of the request.
If you do want to learn more about using PowerApps, check out the videos on my YouTube Playlist.
https://youtube.com/playlist?list=PLQgLuLFqAr9-PoMhLpCWZmtzwgEulKvH5&si=Ryo1kwO_Nr67Ddl0