Bite marks on bottom of leaves, ID please?
 

I saw these "pits" on the bottom of phal leaves and I decided to chop off the leaf just to be careful. As you can see from the first picture it didn't matter as the marks kept on appearing. Do any of you know what this is and how I can deal with it to limit it from spreading to other plants besides the ones already infected and killing whatever is doing this?

This looks like a bacterial infection, not insect damage. Better air movement would help and if you look here for remedies for bacterial or fungal infections you'll find both chemical and home remedies.

Could be a slug or snail.

I would agree with Ron it looks like a bacterial infection.

When it gets dark inspect the plant with a flashlight. Many insects are nocternal, so that's why you can't catch them.

I've read up on the bacterial and fungal damage and it appears that the lesions should be growing if it was bacterial or fungal and they've been on the plants a long time and are not growing at all just multiplying. Could this be some kind of insect? I tried finding it day or night but no luck so far.