Below are the instructions to add users to speed dial in teams
1) Go to the calls tab on the left side
2) Hit Add under speed dial
3) Manually add the users FULL NUMBER. Do not select their user name
4) Click in the box to remove the user name.
5) Hit Add
6) Fill out the contact information> Hit save
It will show as an external number because it's going by the phone number, not the teams user.