Why do they have to transit? It makes sense that only the closest planets would transit. Obviously Pluto or Uranus aren't going to get in the way of you and the sun.
You completely ignore the other parts of the earlier posts!
Mercury and Venus are the only planets that show phases almost like the moon. Why is it so?
When Mercury and Venus appear largest (ie closest to us) they have a shape like a crescent moon and are very close in the sky to the sun (they sometimes even transit).
ALL the other planets when they appear largest (ie closest to us) have a completely full shape (though most are too small to discern) and are furthest in the sky from the sun (overhead at MIDNIGHT).
In other words there is a very big difference in the behaviour of Mercury and Venus from all the other planets that cannot simply be put down to distance from the sun.
Also you claim that Venus and Mercury are closer to the sun than the other planets. Would you please show some evidence for this. I have never seen any evidence for any calculations for these for the flat earth model.
Firstly, we don't see all of the sky over the earth. Much of it is lost to the perspective that causes the sun and stars to set (or perhaps the EA if one subscribes to that). We only see a limited portion of the sky at any one time.
In order to see the phases of the planets, the planet needs to be seen from all positions as it circles the sun. Mercury and Venus are close enough that their small circuits are viewable from many positions.
If the orbit of a distant planet is really big, you are not going to be able to see it in all positions of its orbit around the sun, only when it is over you when it is night and opposite from the sun. Hence, no or limited phases (as in the case of mars).