Phones are the best targets for spying on people: always with you, has a microphone, camera you probably don't cover, handles most of your non face to face conversations and can record the irl ones too, has a GPS, nowadays people even pay with smartphones. They also come with preinstalled OS, usually from a company which biggest source of income is selling user data, purposefully made to be hard to tinker with and glued backplate, which make it hard to remove the battery (although this is mostly because of trying to go thinner, not harder to modify). Just stick to PCs, really.