The image shows as black?
There are hardware limitations on every phone on the max texture size they can display - this determines the largest resolution you can view in the app. Thing is, the max texture size is not a specification that is widely publicized anywhere.
Some phones have max texture size limitations of 4K for example, in which case a 4K render is as large as you can view in the app (or any app, for that matter). You could try the same image at a lower res like 4K or 2K and see if it becomes viewable then, and this will help you find out the max texture size the phone hardware can handle. It would be great if there was a list somewhere with that information, but I've not found one yet, so far only seen the max texture size specs for iOS (which is 4K).
Let me know if changing the resolution of the render does let the image show in the app, and what the make and model of phone is if so.
Thanks!
Tom
PS - if this is the cause, because it is a hardware limitation, there is no workaround, the phone can only handle images of a certain size (as textures), which means any renders you want to view on that device would need to be kept under their max texture resolution size.