Phased array antennas are mostly for getting programmable beam forming, and don’t have much to do with jamming, which works by destructively interfering with incoming waves. Starlink operating on a different frequency means that GPS jammers won’t be able to jam them out of the box, but presumably if they’re jammers built in the last 20-30 years they’d have onboard SDRs which can dynamically hop frequencies. It’s a neat trick to get GPS from Starlink, but won’t stop nation state attackers from jamming access to GPS.