NOTE: The following process requires Windows. Microsoft has not made the options presented on Mac or other platforms.

1) Add a new contact in your TechMail account. You may give it any name you like, such as "Block This Caller". When adding the contact, put the phone number you wish to block as one of the numbers in the contact record. Also, you must specify an email address for the contact so that the appropriate options are available in Skype for Business in later steps. You may wish to simply make up an email address, such as blockcalls@fakedomain.com.

2) Add the email address from Step 1 to your Skype for Business contacts.

3) Right-click the contact that you added to Skype for Business in Step 2, point to "Change Privacy Relationship", and choose Blocked Contacts.

OUTCOME

Incoming calls from that number will not ring on your Skype for Business number. You may still receive notifications in TechMail that you missed a call from that number. However, you may set up a rule in TechMail to move those messages to a different folder, delete them, etc. based on your preference.