There are a couple of ways to test if the focus is at least working correctly:
(1) With the camera in Auto Focus mode, aim at a scene where there is something close and something further away, tap area of the screen where the close and distant objects are visible, and you should see the focus change as below.

(2) Manually adjust the focus, you should see the focus change on the preview image.

If these tests show the basics working correctly but you still not getting the results you want from your photos, then we would need to consider operating conditions. Does the blurred imaging happen always or in certain lighting conditions, inside or out, etc.? Remember that longer exposure times also leave you susceptible to tiny movements of the phone itself.
If you can identify specific conditions in which results are not as good as others, then we have more to investigate, but so far we have not been able to reproduce this concern internally.