If you’ve got curved edges that matter (my iPhone13 doesn’t, but my PinePhone does), it might be worth trying to get a good end-on cross section photo, and importing that into a 2D drawing tool you can use to create that shape in a format your 3D modelling tool can extrude. Looking at my PinePhone, and thinking in OpenSCAD terms, I’d probably model the phone as an intersection of two extruded objects one from the end and one from the side, where the 2D shapes I’m extruding would be as close as I could get to end and side profiles, then use rotate-extrude to make the rounded corners (these look “circular enough” for that, if they were more elliptical, it resize the circular extrusions to suit).

That’d work pretty well for phones (like the PinePhone) that are basically “rectangular prism slabs with uniformly rounded edges and corners”. It’d be much harder to model this Samsung S4 I have here, with its curved ends and it’s compound curved back…