For smartphone night-sky shots, start with the cleanest capture possible: use Pro/Manual mode, keep the phone completely still on a tripod or solid surface, use a timer, focus manually to infinity, and use the lowest shutter/ISO combination that still records stars reasonably well.

For editing, a simple workflow is:

1. Adjust white balance so the sky looks natural.
2. Set black and white points (similar to Levels): darken the sky slightly and raise the bright end enough to make dim stars stand out.
3. Fine-tune exposure and contrast.
4. Recover highlights/shadows if needed.
5. Use dehaze carefully if your app supports it.
6. Reduce noise fairly aggressively, since sky images often have little fine detail.
7. Apply only light sharpening or local-contrast enhancement so stars don’t become harsh.
8. If needed, use selective/local adjustments rather than brightening the whole frame.

If editing RAW files from your phone, apps or software with RAW support are preferable. The community answers mention Lightroom, RawTherapee, Darktable, and GIMP; phone editors like Snapseed or mobile Photoshop can also help with exposure, shadows, noise reduction, and sharpness.

Main tip: don’t brighten the whole image too much—dark sky with visible stars usually looks better than a noisy gray sky.