Set clear expectations at the beginning of the course in regards to expected conduct of all students. This can be done in your syllabus by setting standards for attendance, cell phone usage, tone of discussions, respect for differences of opinion. Also note that all students are expected to abide by the Honor Code and explain what this requires.
State in writing possible consequences for students who do not abide by your stated expectations. Be fair and consistent when addressing possible problems and determining consequences.
If the disruption is a low-level one, you may want to address the entire class instead of singling out certain individuals.
Do not hesitate to address a potential problem early. The earlier that you address a potential problem, the less likely that it will develop into a more serious problem.
If a particular student is being disruptive, calmly and respectfully ask him or her to stop their behavior. It is best to speak to the student privately. You may want to set a meeting for the two of you to speak. During this meeting, share with the student your expectations of classroom conduct and how you perceive that his or her conduct is not in line with your expectations.
If the behavior continues, ask the student to leave the class for the day and inform them that the incident will be turned over to the Honor System for disciplinary action.
Be sure to document incidents and share with your department chair or dean. You and your department chair are always welcome to consult with the Office of the Dean of Students.
Trust Your instincts. If you feel a student is exhibiting behavior that might be dangerous to themselves or others, contact the Department of Public Safety immediately.