"Not trackable" is not quite possible with anything with a mobile data/cell phone modem. Cell companies can query the baseband radio in all phones, even the 2G phones of yore. You can get Stingray'd/ triangulated in theory.

If you are stuck with an iPhone, there is no good way to keep it from leaking data to Apple.

To your question, yes, you can use your iPhone as a hotspot but the data goes through the iPhone. But the connection data is well known to Apple and probably a lot of snoopers. Anytime you use hotspot, there is a global registry of hotspot IPs/MAC addresses. Use a USB hotspot when possible to avoid this.