Suggesting the app "OpenCamera" is basically the right idea. Hower, I would not use the HDR-feature of the app, but turn on exposure bracketing instead. The built-in HDR feature doesn't do a very good job dealing with ghosting which will invariably occur since a smartphone takes up to several seconds for 3 exposures.

With exposure bracketing the photos can be processed (tone-mapped) at one's convenience with a more suitable program. Personally, I'm partial to "Fusion HDR". The summation operator in the free version is easy to use, easy to understand and ghosting is virtually eliminated. For a few dollars, one can buy the prog and gets many more options. For Windows.

http://fusion-hdr.com/

If it must be done on the phone, there is an app by Mark Harman (who created "OpenCamera"). It's called "Vibrance HDR" and offers a number of processing options vis-à-vis the HDR-feature of OpenCamera. However, ghosting is still an issue with "Vibrance HDR". The app can also do DRO, a HDR-like contrast enhancement requiring only a single image. For Android.

https://play.google.com/store/apps/details?id=uk.org.opencamera.vibrancehdr

Worst case scenario, you don't want to bother with HDR. Exposure bracketing still lets you pick the best picture of 3 and avoid blown-out areas you hadn't considered when shooting. To polish that right on the phone, I recommend "Snapseed". For Android.

https://play.google.com/store/apps/details?id=com.niksoftware.snapseed

Here is a HDR drone shot (3 exp) I took while I was out scouting for my upcoming sightseeing video (follow me) on the UNESCO World Cultural Heritage Site "Voelklingen Ironworks". I processed this quick and dirty on my phone with "Vibrance HDR". If you look closely at the vehicles in the roundabout, you will notice the ghosting. In this case, it was acceptable, because the drone - unlike a phone - takes the 3 exposures very quickly and the cars are just tiny viewed from above. (Plus, the shot was just for reference.)