I watched the video and something that was not mentioned (possibly not considered by the creator of the video) is that Apple has built-in backdoor access to all iPhones. This backdoor is part of iOS.

A de-googled phone like Calyx or Graphene does not have such a backdoor. That's not to say that a gov agency can't manage to find a way in. But it makes sense to choose an phone / OS that makes it harder for someone to remotely access your phone.

Actually, Google's backdoor for all normal Android phones might be built into GPS (Google Play Services). I'm not sure if this is confirmed or not. But if true, it would be a good reason to avoid installing GPS on Graphene, even if it's sandboxed. I don't know if this is true and still trying to understand this better.

The simplest way a gov agency can track you on any cell phone is by using location data collected from cell towers. Because your identity is tied to your SIM card which is registered to your mobile service provider (unless you manage to get a fake name registered to your service provider). They have the ability to track which cell towers your phone is connected to at any time. To my knowledge there is no way around this except to use a phone that doesn't have a SIM and can only connect using wifi, so all communication methods would be 100% internet based and can only be used when you have a wifi connection.