Time to repot Phalaenopsis keiki? Several considerations.
 

Alright, so in my last post someone told me my keiki should have at least 3 inches (minimum) total root length before repotting. I measured these roots several times just to be sure. They are exactly 3 inches long--not a bit more! There is one on the other side of the main root you see in this picture about the same length, and a nub which is about a quarter of an inch long or so. So only two very developed roots. The small little nub has been growing quite quickly! However, I am hesitant and eager to pot it at the same time. The larger roots are a bit wrinkly and not as full as they were when I first bought the Phal. I'm worried I am going to lose the keiki if I don't repot it, or I will lose these roots because they are drying out. I tried misting them for a while. I am not sure if that was the correct thing to do or not, but I stopped because I was worried the water droplets might intensify the light and cause sunburn on the roots. The other side of the left leaf is a little wavy, but still glossy and a nice grass green color. The keiki is at the very top of the largest flower spike, of which this Phal has four! This spike is about a foot tall whereas the others are much smaller. The plant's roots are recovering from a bit of root rot (which it had when I bought it), so I'm thinking it would be better for the mother plant if I take the keiki off so it can concentrate on the new root growth just below the crown. I have it potted in the AOS potting mix which I really like (I tried that miracle grow stuff for a while, but know I know that stuff holds far too much moisture!!). I plan on potting the keiki in a very small clay pot with presoaked sphagnum moss. Obviously my question is, will the keiki survive if I pot with just 3 inches of root growth? Or should I wait?
One other question-- those teeny branches growing out from the main spike--what are they? Will they develop into some thing else? Is it safe to remove them from the flower spike with the keiki? My run of the mill mini phal has nodes but doesn't have any of these branches/cluster-like things growing from the spike.

As you can tell, I'm still quite a beginner with orchids so I thank you for any and all help!

The branches on the spike look to me like a secondary flower spike. So your phal is going to bloom again. I generally leave my keikis on the mother plant for a long time as long as the spike is still green. I mist the roots on the keiki every time I water. The water droplets will not cause sunburn but be careful not to get too much water in the crown of the mother plant. I have some keikis that have been on the mother plant for two years. On the other hand, if you really want to repot it, it probably has enough roots to survive. Personally, I would wait.

Is this how phals make more plants? Or only certain phals?

Some Phals, as well as some other types, keiki freely. In some cases, an orchid may get keikis as sort of a last gasp effort to reproduce when the plant is in poor condition. But often, plants are in good health, and have the resources to support making babies.

Some Dendrobiums (the kind that want a cool dry winter rest) will develop keikis instead of spikes if the winter requirements aren't met. But they, and other Dens, often keiki quite freely as well.

Epidendrums, Vandas, some Tolumnias also can keiki freely.

So, yes, it's another way orchids can reproduce.

Oh. Okay. That makes sense than.

How big is the (Pot Size) has to be when is time to get the Keiki off the mom? I know it can't be too big or the baby roots can suffer? What's the best size for the baby pot?

I think I would wait a bit. The keiki itself is rather large looking so the roots look small to support it on its own.

Usually you would use a pot size that fits the roots. So in this case a fairly small pot. It could be a bit larger since the roots may develop fast and you don't want it drying out every day. But too big invites root rot as the media doesn't dry fast enough.

I have seen them come in on the spike and what was done...the spike (it was a secondary branch, keiki was toward the end of it) the planted it still attached to the mother but in its own little pot...they left it for the nutrient reasons and when it was big enough just had cut the spike. just an idea..
i have on coming in on my phal....buy near the leaves in between 2 leaves.... :) good luck