The device is where everything else lives. A hardened browser on a compromised laptop protects nothing, and the phone in your pocket is the most complete surveillance record that exists about you, location, contacts, messages, photos, and sensors, in one place.
These guides work with the devices you already own. Specialty hardware and alternative operating systems have their place at the far end of some threat models, but the first 90% of device privacy is settings, updates, and encryption on stock equipment.