It isn't just saving money: in the case of phones it is keeping you in easy contact. Having Teams/Slack/other on your phone so it will beep you when the company has a problem you could look at. A good company will be flexible in reverse so you can take that bit of time back when you need to, but many are not this decent so you are giving them your attention/time/effort for free.
The company could provide a device for that of course, but people often don't want that or it isn't reliable: they don't want an extra device to carry around, they don't remember to keep it charged, they forget to take it with them far more often than their own phone, ... So as well as the cost aspect BYOD can make thing more convenient in other ways.
The company could provide a device for that of course, but people often don't want that or it isn't reliable: they don't want an extra device to carry around, they don't remember to keep it charged, they forget to take it with them far more often than their own phone, ... So as well as the cost aspect BYOD can make thing more convenient in other ways.