The present concerns are not relating to 'significantly higher frequencies' but to C band, between 3 and 4 GHz. The precise relationship between the mobile and aeronautical services is documented in detail earlier in this thread. There are indeed long term plans for much higher frequency bands for 5g, but they are still in the field of research.
As for interference to GPS, the new cellular band at 3GHz is much further from the GNSS band than the older cellular bands. There doesn't seem to be any interference related to to those. Indeed modern smartphones have cellular radios and GPS receivers working within the same device.