If the Pats had claimed Phillips for the active roster, his maximum cap hit for the remainder of the season would've been $788k, minus the remaining salary of whoever was moved off the roster to make room (unless it was someone sent to IR, in which case, some portion of their remaining salary would still be hitting the cap, if not all of it). That would've sucked up a lot of the current cap space of $1247k, but still do-able without making an immediate move with a current player's contract.
If the Pats had claimed him for the PSquad, Phillips' cap hit would've been only $99k for the remainder of the season.
Some acquisitions are, indeed, realistically do-able. Others, not so much.