Hey @Bill Hayward8, thanks for your question!
Any navigational, geocoding or mapping tools on phones will rely on the GPS accuracy of the device. In the case of what3words: GPS gives your device latitude/longitude coordinates and then what3words converts those numbers into a what3words address.
GPS accuracy on devices can vary if the sky is blocked by trees/ you are indoors etc. You can zoom out of the grid map to see if your blue dot is in the correct square (it will be more or less around the same place) and if not, you can tap the closest, most appropriate square and share that what3words to be more specific about your exact location.
I hope this helps!