System 3075 paused for a moment before saying, "I am already bound to your phone. Unless the phone is destroyed, the system cannot leave it."
Actually, it could have done what Ruan Shiyu mentioned earlier—taking root in her mind and speaking from there. However, since many systems were custom-ordered by future humans for their ancestors, they would travel back together into a technologically backward ancient society. The people of that era lacked the technology to fully control the systems, so to prevent the systems from doing anything excessive, restriction programs were pre-installed before they made the trip.
Operating solely within a smartphone was one of these restrictions.
Chapter 89