You can find old DOS games here ---> https://www.abandonwaredos.com/, or just google "abandonware dos games"...
there are plenty of these websites, you can also buy remastered versions at GOG and similiar services.
JS-DOS will not work natively on mobile devices but you could plug in some mouse and keyboard with the right adapter...
Create a .zip and put your DOS game files in.
Make sure your game is not in a subfolder inside the zip file.
Load it and play. Large files will take more time to start the emulation.
To override the default dosbox.conf, just create a new dosbox.conf file inside your game zip.
Thanks to: Js-DOS Project