Best phone for good quality pictures

There is no phone camera that gives GREAT picture quality. Sorry.  Some are slightly better than others but none are as good as a dedicated digital single-lens reflex (DSLR) camera with interchangeable lenses.

• What is your budget?
• What kind of pictures are you thinking of taking? 
• What will your pictures be used for mainly  -- prints, social media, online website, selling through Stock photo sites, etc...?  Please be specific.

If you're interested in developing your photography skills in order to be a successful stock contributor, take the money that you would have spent on a high-end phone and spend it on a DSLR. There are many sites where you can do research on cameras and lenses. You don't need high-end professional level equipment in order to capture images good enough for Adobe Stock. What you do need is some basic education on composition, lighting (or use of available light), and editing - and lots of practice !

The best phone or camera is one where the person behind it knows the basics of composition, light and how to operate his camera.

It may be worth mentioning, if you are new to commercial photography, that it is a challenge to get world class photography to Adobe's standards from a phone, thanks to a combination of small sensors and aggressive consumer level optimization. A serious phorographer will also have a number of serious cameras, that are just cameras. Commonly, but not only, SLRs, which will cost more than even a top phone.

Are you intending to become a contributor?

There is no such thing like a best phone for something. There isn't even a best camera.

There is, however, one indication towards quality. Size matters. The bigger the sensor is, the better the picture quality gets. Drawback? The price gets higher. In my eyes, phones do take great pictures, but looking into the quality, you will not get pictures with phones that are high quality enough for some applications. 

Try to get real world test images of an interesting phone/camera and check image quality at 100% and 200%. If you see artefacts that you can't correct, then the camera is not suitable.