This app was mentioned in 2 comments, with an average of 1.00 upvote
I have this on my phone - it's not perfect but it gives a good idea of what sort of framing I can get. Used mostly when I don't have a long lens and wonder if it'll be worth coming back when I do. (wide lens visualisation is understandably a bit useless)
Focal Finder for android. I like it. Not free but only 99cents. Zoom in and out or set red outlined presets for specific lenses/focal lengths.