First of all which phone and phone operating system are you using?
This how it's done in WM10:
- Tap the elipsis menu
- Tap select calls
- Tap the boxes next to the calls you want to delete to tick them
- Then tap the trash can icon
If you need additional help or have more questions or details to share, please join the site so you can reply in this thread. See
this link for instructions on how to join Windows Central.