Civilian-use GPS signals are unencrypted specifically because they want to be as open as possible. It was originally a military only system, that was only opened up in 2000 after a civilian airliner blundered into Russian airspace and got shot down.

Military-only signals are encrypted. There are also newer civilian-only signals with checksums and on alternative frequencies but there aren’t enough of the new sats up yet to live on it fully. Check whether your phone supports dual-band GPS, or specifically the L5 signal. There are even apps you can download that will display the full output of your GPS chip, including every satellite in view.