Using a company suppression is a very straightforward process in IntuList. This video will walk you through it.
What happens if my suppression data contains phones or emails that are already in my database?
Phones or emails added via the manual entry form, if already present in your database, will also mark those leads to never be sold/exported at any point in the future. Adding existing (i.e. leads that had already been stored in your system) suppression data via file upload will NOT mark those leads for no future export.
If you simply want to add a few phones or emails to your suppression file, just use the manual entry form. It is much faster than first entering those records into a file and then uploading them.