A tripod isn't necessary, but what IS necessary is holding the phone very still when taking the picture. OIS can help, but can't eliminate "camera motion blur". It seems to do best with video.
Unfortunately, phones aren't designed for picture taking, and touching the screen to take the picture often results in pushing the camera forward while the picture is being taken.
Practice holding the phone steady when taking the picture will help with camera motion blur, but no with subject movement.
edit: A tool like this can help take steady pictures:
https://www.bhphotovideo.com/c/prod...tml/BI/20079/KBID/13844/SID/UUacUvbUpU5973988