What kind of orchid is it?

Phalaenopsis.

The only time I've seen a phal get 4 yellow leaves at once it was dying from frost bite. You have new growth so it doesn't sound like the plant is dying but it may have been severely stressed. Could you have sun burned it when you put it outside? If you had root rot because of too much water than it may have sacrificed the leaves to conserve energy and help deal with the more extreme outside conditions. This is all guess work. If you can post a photo that would help.

I agree with Claire. It sounds stressed, probably from too much or too little water. Since it has new growth, it hasn't died. Just monitor it. Are the leaves still very secure to the plant, or if you touch them do they feel loose?

Sarah

If your plant is outside, is it protected from getting water in the crown? Phals hate water in the leaf axils and it must be wicked out with the corner of a tissue or a paper towel. If outside, the plant should be covered somehow to protect it from the rain.

Is there a chance your night temps dropped below 50F or so. That might shock the plant into yellowing and dropping its leaves, but not enough to kill it.