Is my phone's GPS limited by US regulations?
No it's not.

Commercial GPS receivers (like the one in your phone) only work below 18 km and below 515 m/sec. The rationale behind this is that this way they can't be used in ballistic missiles (yes, I'm serious.) 

In order to circumvent this you'd need to flash a different firmware to your GPS chip, if you didn't do this you're safe. No current android device ships with munitions grade GPS receiver.