In addition to number 1, eight other speed dial numbers can be assigned on the LG smartphone. only contacts that have been saved can be dialled as speed dial numbers. it is not possible to freely enter a phone number. it is also not possible to change or delete number 1 (mailbox).
Android 9 | LG UX 9.0
Step 1:  Open the  Phone -App
Step 2:  Open the  Menu
Step 3:  Tap on  Speed dial
Step 4:  Tap on a speed dial  number
Step 5:  Choose desired  Contact
  1. Open the Phone-App
  2. Open the Menu
  3. Tap on Speed dial
  4. Tap on a speed dial number
  5. Choose desired Contact

LG Instructions