When you in your call log, click on your menu button (3 dots in the upper right corner), you should see a select multiple or select all options in there. Another possible way (not 100% familiar with this specific device, but from my experience with other Android phones) is by pressing and holding on any phone number in the list and it might give you options to select multiple or bring up boxed where you can check the numbers you want to remove.
Please let us know if you have any other questions.
Did a post have a solution that worked for you? Help other people find solutions faster by marking posts that helped you as an "Accepted Solution". Learn about accepted solutions: Learn More.
*I am an AT&T employee and the postings on this site are my own and don't necessarily represent AT&T's position, strategies or opinions.