A check box under SLP/Experience/Results/Appearance titled “Use Dial Link for Phone” when checked makes the phone number in your locations results clickable to auto dial. This feature is available exclusively with the Experience Add-on (also with Premier)
It will vary based on how your browser handles location sensor requests. Not all browsers support location sensor, and some do not give a visual indicator if the location sensor is disabled for any reason (security, user preference, etc.).