GPS accuracy of standard phone chips is limited to a few metres . You cannot get better than that because of the technology employed. However, when travelling by plane, you’ll have noticed that often GPS position is lost once your plane reaches a certain speed, which (so I’ve heard) is due to the processing capabilities of phone chips. So, to make sure that you get the best possible signal, and as a bonus continue using GPS on flights, you could buy the “Dual XGPS150A Bluetooth GPS Receiver” . Costing about $100, it doesn’t give you better accuracy, but might give you a better antenna position. Until recently, this was the only reasonably priced option to make the most of the standard technology.
Around 2015, there were movements towards lower-cost GPS RTK solutions (using a base station) , , . However, a base station is awkward, and systems would cost several hundred dollars. There were also some noises in 2016 about software-based improvements , but it’s not quite clear to me what became of this.
With this solution one could, in principle, get higher accuracy on GPS by using dual-band GPS. Solutions again were a few hundred dollars and not meant for consumers. Moreover there were issues around the chip design, meaning that the technology wasn’t ready for consumer-type applications for various reasons; not until late 2017, when Broadcom introduced the “World’s First Dual Frequency GNSS Receiver with Centimeter Accuracy for Consumer LBS Applications”, i.e. the BCM47755 chip , , . .
However, it wasn’t clear which phone would use this first, until June 2018, when the first phone featuring the chip arrived: the Xiaomi Mi 8 . . GSMArena states that the phone has dual-band A-GPS, GLONASS, BDS, GALILEO, QZSS . The phone costs around $500 . So for what was the cost of a higher accuracy GPS system previously (that’s not necessarily all that easy to use), you’re now getting a phone with possibly 30cm GPS accuracy.
But wait – this article  (by the author of GPSTest ) reviews whether the full capabilities are enabled yet. It doesn’t seem to be the case right now. However, no doubt this will happen soon for the Mi 8. Moreover, other manufacturers will no doubt follow suit, and use these higher accuracy GPS chips in their flagship phones.
What have we gained? Clearly a few metres of accuracy tell you the road you are on, but not the lane. It doesn’t tell you where the pavement is, nor where the row of houses starts. So it works for getting from A to B, but if you need to be in a specific lane, it’s tricky. So for travelling, you’ll now get the lane you’re in. For mapping, you can now map many more features from GPS.
It will be interesting to follow this story about innovation and putting more power into the average user’s hands!