Depends on smartphone (and smartwatches). Not all have it, at times it disappeared from brands that had it earlier.

The smartwatch series I use explicitly include it because it's essentially the "all in one" version in a series that had smartwatches designed for aircraft use (including military versions where they serve as backup cabin pressure warning, apparently)

Smartwatches include barometers because they enable elevation measurement far more accurate than than GNSS (GPS and GPS-alikes, they tend to be noticeably less accurate in the vertical than in the horizontal). In particular when both are combined: barometry for high frequency changes (going up a hill) continuously calibrated against a long term average of the GNSS elevation to filter out low frequency changes in barometry (weather influence).

But back to device could weather observation, this would require continuous GNSS, devices don't do that (network location would not be good enough).