I didn't lose any data but I did have to try to find my internal username and password for the database access.
Note that the phpGedview folks advise that you will also need to Upload the GED file to make sure that all links have transferred correctly. So download it first to make sure you are working with the most up-to-date file you have. And When you are Replacing it, tell it Yes to Retain Media links or you will have to build them all again. You may find that you have to renew the permissions for the users too. I had to do a couple of them but not all of them.
These are perhaps better wording...
"As part of the upgrade, did you first export your database from the old installation?
This creates a GEDCOM that contains the media information. You then have to
import that GEDCOM into your new installation, telling PGV to erase all old
database data and not keep media links.
These instructions have been echoed over and over again in this forum. In your
particular case, you should simply have done an upgrade-in-place.
Some of the missing tables are created by various modules, such as the Research
Assistant."