Here's a working "Phase Gate Scout" ability I made from the old PhaseScouts mod, it works with 1.17 and Entrenchment:
What it does, is all visited planets are marked as phasegate points.
If you could make it a timed effect, and somehow project the effect to the target system, it could work, maybe you could make a novalith cannon-like projectile with the effect. So the entityBoolModifier "IsPhaseGateEndPoint" would apply to the local system, at the same time a very fast projectile would be fired to the target system (check BuffTechOrbitalCannon), and the projectile would make a "IsPhaseGateEndPoint" effect there, the ship could fly between the 2 systems, and then the effect would wear off.
Well, I'd be interested in such. It would make my Borg Cubes like really using their Transwarp engines
Edit: Ah, yes, this is exactly the same that EvilTesla wrote... and I thought I'm so smart