One plus 3T - Manual (Page 19)

19 | What’s in the Box Device OxygenOS Safety Information
Dialer
Tap the on your home Screen or application drawer and use the dialer to make phone calls manually, or tap any contact card from
the Speed Dial list to quickly dial that contact. Select a phone number from Contacts, an e-mail, or a text message to make a call.
Contacts are automatically added to your Speed Dial list based on frequency of use. You can permanently pin contacts to the top of your
Speed Dial list by marking them as Favorites simply press the star icon on each contact you want to add.