Those sensors you are referring to are not reliable enough to tell elevation accurately. In addition to that, buildings may have different pressure to the outside

They are sufficient if you have other phones in the same vicinity at known locations.

If bobs phone is 10 meters higher than alex's phone, and they're in a 2 floor building, bob must be on the top floor and alex on the bottom.

This principle can be used at scale by people like apple and google.

i have successfully told the difference between the ground and 3rd floor with a galaxy note 3's barometric sensor(for triggering home routines only when actually at home vs just arriving at the location)

maybe that was just a particularly good sensor...

My 2013 Moto X has a barometric sensor. When graphing the raw sensor output, I can see a ~6ft elevation change with little difficulty.