I think it needs to be a separate unit, and not merged with SBs because people are right; it would be overkill for an SB and smaller raiding/scouting forces would be useless. Instead, keep it as its own structure, but extend the AOE to the whole gravity well. Make it ACTUALLY 'inhibit' phase jumps though: ie NO ships jump... the invaders, or your own ships (including trade/refinery vessels). But make this an ability that needs to be turned on or off.
To that end, your PJI has two modes: on, and no ships jump, or off and all ships jump. When it's off, give it a heavy shield, but when it's on, all power is required to maintatin the inhibition field, so it has NO shields, and is thus vulnerable to attacks.
I'm going to make this my last post on the PJI issue, because I want to explain my train of thought:
* A node-blockade PJI is a powerful defensive tool/option.
* Its goal should be to keep a raiding fleet from roaming freely around your inner planets, which traditionally have much lighter defenses than your border planets.
* To actually be the useful tool, it needs to not be paper thin so it can't get destroyed without at least some effort.
A separate PJI structure fails the last point. With the carrier changes, and general lack of quick anti-strikecraft capability of stationary defenses, it is fairly easy and fairly safe to destroy the PJI with bombers. You'd need more squads if there's a repair bay around (which there will be), but even 10 bomber squads (5 carriers, 3-4 if Advent) should be sufficient to take it out with a repair bay fixing it, in most cases.
As such, the node-blockade PJI becomes utterly ineffective because it can't delay hostile fleet movement long enough for your own defensive fleet to have a chance of getting there. It may be powerful in principle, but if it's too easy to destroy it will be useless.
Enter the Starbase. The goal here is to put the node-blockade PJI on something that can take more than a few bomber squads and survive, but at the same time be weaker and easier to destroy than a Starbase with another "super" upgrade. Going by your idea, researching the PJI upgrade can decrease shields on the starbase due to the power requirements to maintain the field, and at the same time it will also lock out some cool super abilities that other starbases can get (Vasari get debris sucking/damage shield, Advent get the meteorites as examples).
This way, you end up with a powerful effect that's useful at the same time because it can't be nullified with as little effort as a separate PJI structure can be. The Starbase with the node-block PJI is weaker than its fully-military counterparts, but you get good use out of it. If the node-block PJI is its own structure, it not only can be spammed several per planet and on each planet (which is cheesy regarardless of how effective it would be) but a single structure could also be destroyed too quickly for it to have much effect.