You cannot create a mobile phone where you are not tracked. Even if every single piece of software in every component were 100% libre (which is actually illegal; some proprietary software is required), or if realistically you isolate the required proprietary software to have no access to any of your details or location, the phone networks can track you simply because of the way the cellular network is designed.
They use weasel words to dodge a point that I mentioned above:
We intend to invest time and money toward freeing any non-free firmware.
Yeah, I'm sure the will "invest time" into looking at the illegal possibility of replacing the code running on the modem, and then immediately reject it. Purism already has no credibility as it is. If they want to get any of that back, they need to start being frank and honest about this: they can supply a phone with a 100% libre OS, isolate the modem so it can't investigate or tamper with anything, and include a libre bootloader. This would be basically speaking unremarkable; the only reason it would be interesting is no mainstream company is doing it (or rather, none of them are doing it and telling their customers that they're doing it), and there's certainly no reason to limit such a simple thing to a $600 price point.
It's very likely that any such system will have no hardware graphics acceleration, no WiFi, and no Bluetooth; firmware blobs would need to be added for the wireless in most cases, and a proprietary driver for hardware acceleration in most cases. It's plausible (but not likely) that one or more of those issues may be resolved by a combination of choosing the right SoC and reverse-engineering. But given Purism's history, I doubt that will happen.
Overall, I don't think it would be any more wise to get over-excited about this project than it was to get over-excited about the laptops. I'm not opposed to the idea, but it's really not worth that much, and definitely not worth a $600 price tag.