There is a reason for everything, so what is the reason some prefer to phone with the left ear and others with the right ear?
The results of this study add to a growing body of evidence that the left and right ears demonstrate asymmetric function reflecting the expected hemispheric asymmetry and that the asymmetry is based on the type of stimulus being processed. These experiments demonstrated that when stimuli are presented to the left ear, a slight but consistent advantage is shown when processing tonal stimuli as was seen in previous studies of gap detection
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3294255/