This is kind of a weird example to begin with on a forum mostly populated by software engineers, because I'd find it very weird if a manager ever objected to someone using their personal phone at a SWE or similar office job, but I'd guess that the sets of jobs where a "boss" would object to someone using their phone during work (but still getting their work done) and those that would potentially have a company phone are mostly disjoint... a complete prohibition on using your phone seems like entry-level retail job type rules. excepting corner-case stuff like some very high security facility where you wouldn't even be allowed to bring any outside electronics in.