The phaseout applies if the business is a Specified Service Trade or Business (SSTB). Does your client's business fall into this category? If not then there is no income phaseout. If the activity is a SSTB then make sure you check the box indicating this on the input sheet. The location of the checkbox for SSTB depends on where you are entering the info.

You mention Guaranteed Payment to Partners so I assume you have a K-1 1065. On the input sheet for the K-1 enter all the numbers provided to you from the K-1.  On line 20Z quickzoom to the input sheet where you will be able to provide the QBI details including SSTB options