According to the discussions in this forum, the formula of trade income seems to be:

constant A * No. of trade ships * No. of Jumps of the longest direct trade route (shown when you mouse over your credit'

or

constant A * No. of trade ships +  constant B * No. of jumps of longest direct trade route.

Either way, No. of jumps of the longest trade route affect the trade income whether as a direct multiple or a added bonus.  Ever since i knew this , it occurred to me that phase stabilizers could reduce the number of jumps of your  trade routes.

So I paid closer attention to my trade incomes before and after i start building those phase stabilizers. In the game i was playing against AI as Vasari on a medium map 'entanglement' (something like that) i expanded more or less linearly and built trade stations on each planet to form the longest trade lane that spans my entire empire. That gave me around 10.6/sec. I am 100 % sure that i did not loose planets or trade station that breaks the trade lane afterwards. However, once i built those phase stabilizers on some of my more important planet, my trade income decreased to around 9. I noticed the longest trade lane now go through my phase gate planets and trade ships fly along them. THIS  ACTUALLY REDUCE THE NUMBER OF JUMPS MADE BY THEM.

As a matter of fact, if you have expanded normally from one planet to another and attempt to exploit the longest trade route bonus by making a long chain of trade routes, building phase stabilizers will almost always reduce the number of jumps made by trade ships because they always provide more direct means of travel.

There are rare exceptions. When your empire is completely segmented by allied planets without trade stations or colonizable yet unbuildable (logistically) dead asteroids. Phase stabilizers can help you connect these pieces of your empire to create longer trade routes. Normally this is not the case, so the above case is more common.

Ironically , these phase gates are built to facilitate transportation. Yet, they reduce trade income.... Also, i noted that refinery ships do not make use of the phase lanes created by stabilizers, so they still only harvest mines that are 'naturaly' one jump away.

I know Vasari is not about trade and phase gates have those dark armada tech that give you free stuff that may even be scuttled but dark armada is some sort of endgame tech (some say it needs a nerf) nor do i like the idea that Vasari always have to rush to them. I'm fine if Phase stabilizers dont improve economy because of the mobility advantage they give to your fleet.... but a penalty? This sounds like building a Suez Canal that reduces trade income.....