I think they have been using the arbitration estimates from MLB rumors. Cot's does this and has $18.2 million left to spend with an $11 million arbitration estimate.
One thing the Phillies could do to get a little more room would be to agree on a 1-year deal below that estimate with the understanding that the money would be made up in the subsequent long term deal where the AAV would apply to 2021 and beyond if the deal were signed after opening day.
Cots: