If you want to make a call by tapping one key, you need to assign the contact to a speed dialing key. But first you need to save the contact in the address book.
Find "Speed dial settings"
Assign contact to speed dialing key
Tap the phone icon.
Tap the menu icon.
Tap Speed dial settings.
Return to the home screen
Tap Tap to assign a number next to the required speed dialing key.
Tap the required contact.
Tap the home icon to return to the home screen.
*Please refer to the Sony website for more information or further support.*