To access the speed dial function on the p168s, go to the main menu, then “Call Center”, then “General Call Settings”. Speed Dial will then be Option #3.
To use it is just the same as on the other p168 phones, hold down the number at the call screen, or just type that number and press send to call the person that the speed dial number is set to. The number needs to be in your phonebook to set it to a speed dial digit.