Google has held a couple of GPS precision challenges for smartphones, and Galileo recently launched their High Accuracy Service (HAS) for high accuracy Precise Point Positioning. Android has built in support for full GNSS phase measurements. Smartphone positional accuracy is already pretty good with L1+L5 bands, and it will probably get even better soon.

https://www.kaggle.com/competitions/smartphone-decimeter-202...

https://www.euspa.europa.eu/european-space/galileo/services/...

https://barbeau.medium.com/gnss-interrupted-the-hidden-andro...