For general aviation small aircraft flying VFR under 10,000 feet, can I use my phone GPS for navigation in the US?
Can you do it? Sure. It is recommendable? That depends.

If you are planning to use it as your primary source of navigation, then I would say definitely no. Aviation GPS units are designed to be used on aircraft, they are reliable and have airspace maps. There's a reason they are expensive. The same cannot be said for your phone GPS.

But, if you remain aware of your position by other means (visually recognising landmarks and cross referencing them with aeronautical charts) then sure, you can use your phone GPS as an additional source of navigational information.

Just keep in mind that if the GPS suddenly fails, you should be able to continue the flight normally. If you can't, then it means you are trusting the GPS more than you should.