By ANDREW DeMILLO Huddling for safety in classrooms as gunfire rang out, students at Apalachee High School texted or called their parents to let them know what was happening and send what they thought could be their final messages. One student texted her mother to say she loved her, adding, “I’m sorry I’m not the best daughter.” The Georgia school shooting that left four dead and nine injured last week was every parent’s worst nightmare, and one that highlights potential downsides to efforts among states, school districts and federal lawmakers to ban or restrict access to cellphones in classrooms. The moves to restrict phone use in schools have been driven by concerns about the impact screentime has on children’s mental health and complaints from teachers that cellphones have become a constant distraction in the classroom.