Using a smartphone won't result in mental health problems for most people, but excessive and compulsive use could worsen anxiety and depression symptoms.
Virtually every domain of clinical psychology finds that smartphones threaten our psychological well-being. Findings include increased anxiety, depression, suicide, bullying, eating disorders,...
Excessive smartphone use is associated with depression and anxiety. Theories such as Compensatory Internet Use Theory are discussed. In the present paper, we examine the literature studying relations between problematic smartphone use (PSU) and anxiety symptom severity.

Furthermore, visual representations like the one above help us fully grasp the concept of Mobile Device Anxiety Symptoms.
Its called nomophobia: a fear of being away from or disconnected from mobile devices. Researchers believe that nomophobia-related stress stems from smartphone users feeling socially threatened without online connectivity. Ironically, those who have nomophobia are also likely to report loneliness.
This review paper investigates 1) the functions and characteristics of mobile digital mental health care applications for the treatment of anxiety symptoms, 2) extracts common attributes of the applications, and 3) compares them with existing traditional treatment mechanisms.

Excessive use of smartphones can cause unhealthy physically and mentally. Feeling of discomfort include physical discomfort and feelings of loneliness, anxiety, and depression. Measures include controlling smartphone use, strengthening self-control, and engaging in physical exercise.