Fix your posture.
Most of us are at risk of back pain due to our sedentary life. Furthermore, using one side of your body more than the other also adds to this risk. Therefore, realigning your spine by using both sides of your body equally will only be beneficial for you.
The posture you develop from consistent use of smartphones while walking can lead to a variety of physical problems such as neck and back pain. Furthermore, it makes a bad impression on others: you will look less in control and less equipped to handle stress.