Turntable leveling

noromance

... because I can detect 0.25mm VTA

Not likely, especially because common LPs aren't flat within .25mm. If you're convinced you can hear a deviation that slight, it suggests that your stylus may be chipped or damaged. That could account for your claim.

I use an "analog" bubble level, and that seems fine.  So my answer to your question is don't fret over it.  On the difference between your phone app and the ordinary bubble level, I'll go with the latter.  I have an "audiophile" bubble level, meaning you center an air bubble in a circle, unlike with a carpenter's level, where you need to level it in two directions. If the bubble is just barely touching the inside of the inscribed centering circle, that's acceptable to me.  If the bubble edge lies outside that circle, I adjust to correct.

something to also consider: is the tone arm level to your plinth. good idea to make sure both are true to each other so when you level the whole table everything is true to each other. Not such an issue with tables that have an arm mounted by the manufacturer, but if you've added another arm defiantly check that it is leveled to your plinth.

 I ran into this issue when assembling my Garrard, the Jelco arm (750L) as good as they are have terrible VTA Adjustment that can and does change the arm level to plinth when tightening the VTA Set screw.