Hi! So a phone could well benefit from RTK, but this is a local signal, so you have to pick up something that is relevant for your location. Meanwhile, the High Accuracy Service broadcasts realtime corrections, but it does so on a frequency band that is not supported by phone handsets. Also, the RF conditions in most urban environments are such that I'm not sure such corrections would be received well enough to matter in most cases. Phones are moving to dual frequency chipsets which will also improve accuracy without further help. Hope this helps!