Are you not from the US? Being "on call" is pretty common in certain professions. Doctors, for instance. A lot of vital IT workers are on call all the time. If a server goes down in prod, who are they going to call?
However, the woman in the article was a sales executive, not an IT worker. If the company had to be able to reach her in rare emergencies, they could call her on her personal phone if her company phone was turned off.
"If a server goes down in prod, who are they going to call?"
In the good old days, before companies got cheap, they used to hire three shifts of operations staff who worked 8 hours each.