Android 6.0 or higher
Your phone must support DNG / RAW and manual settings (ISO, exposure time). The app checks the support of these functions upon startup.
You can use a simple mount for travel purposes like iOptron SkyTracker, AstroTrac or StarAdventurer. You put a ballhead on the top and add a clip from a small phone tripod. With the preview function (which is automatically visible after start) you can adjust the ballhead according to the brightest stars.