Stored speed dial numbers can be called on the Samsung device by tapping and holding the respective digit on the dial keys. For speed dial numbers of ten or more (i.e. two digits), the last digit must be tapped and held down.

Example speed dial 145: Type 1 and 4 as usual as phone number, then type and hold 5 to start the call for speed dial 145.

Android 11 | One UI 3.0
Speed dial numbers - Tap on  Phone
Speed dial numbers - Tap and hold a  Speed dial number
Speed dial numbers - Choose a  SIM card   (Dual SIM)
  1. Tap on Phone
  2. Tap and hold a Speed dial number
  3. Choose a SIM card (Dual SIM)

Samsung Instructions