You can add a number to the Spam Number list directly from your personal inbox. All you need to do is to make sure that you are in the Inbox Tab and find the spam number you want to block.
Once you find your target, click on the existing message with that person, the menu will look like this:
Press the Actions button above the conversation. Scroll down to the option "🚫 Mark as Spam". When you select this, the phone number will be added to your Spam list. That number will now be blocked from texting and calling you.
All of the phone numbers marked as SPAM can be found in the Spam Numbers, visible only for the Administrators of your smrtPhone account.
You can read more about adding a phone number to your Spam list here.
To remove a number from the Spam Number List:
Find the number within the list
Click the delete button (trash can icon) next to the number
Confirm that you want to remove the number