yes. If you enable pressure sensor, then altitude value is not coming directly from GPS, but is improved by values from pressure sensor.
What do mean with improve?
Why do I ask: Recently I was on a mountain hike, I had wonderful weather and I guess pressure was quite stable.
Calibrated the pressure sensor at a height of 840m, hiked up to the summit at 1889m (according map and also to my knowledge) but Locus recorded in the track a max. height of 1832m

.
Then I returned to the starting point at 840m and Locus recorded 849m in the track which I could agree due to may be changed pressure (6hours later)
So then, phone should be also quite precise and usable (in term of relative altitude, absolute altitude will still not be much precise)
I understand that relative altitude is calculated from pressure difference and added to absolute altitude from pressure calibration procedure.