Based on a quick perusal of Artlcle XIX of the CBA, I think you're correct. The Phils' options w/r/t Robertson are: 1) Keep him on the roster, and put him on the 60-day IL in March; or 2) ask unconditional release waivers on him. If they ask waivers and he's claimed, his contract goes with him. If he's not claimed, he's released, and the Phils pay him $13 million (2020 salary plus 2021 buyout).
Since I seem to have opened this box, here are some summaries:
Eight free agents (as of 9 am this morning):
(The Phils could - theoretically - make Qualified Offers to Hunter, Nicasio, or Rodriguez - but they won't!)
Three players with club options that could be declined (deadline for decision is 5 pm next Monday):
The 15(!) players who are arbitration-eligible (some of whom may be non-tendered) (tender deadline is December 2nd):