Could be insect issues or the solutes left behind after a natural process called 'guttation'. Al

It's a good possibility it's some kind of insect. Wipe the leaves with rubbing alcohol and/or liquid soap instead and see if it disappears. Nick

I've never seen sap under a phal leaf without finding culprits, tho sometimes you have to look and look til you find them, and they are excellent hiders. The question is where to look, and the answer is look everywhere one of the little buggers can hide. Aphids usually go for tender new growth and wouldn't be on the relatively tough underside of a phal leaf. So look for mealies (white cottony blobs) or scale (bumps that slide off-- ie clearly are not dings). They are hiding somewhere pretty successfully, or you would have seen them already. So look under the leaves, and especially in the junction where the leaf attaches to the stem. It's astonishing the places they can find to hide. I have found them in the leaf junction of a tiny old seedling leaf still hanging on to the stem of a fairly biggish phal, but hidden away below now big newer leaves. Bend the leaf back as far as you dare without breaking it to look inside. I have even found them nestled in the center of a tiny new leaf, the devils. They also hide out in the nodules on a flower stem. I once had a recurring infestation of mealies on a spike of a Doritis hybrid. Those spikes last and last, and the infestation kept coming back, always on the flowers (they *love* flowers). Finally, I cut the flower stem and peeled the covering off the nodules on it. Sure enough, every undeveloped nodule had mealies tucked inside ready to get on the flower when it developed. So check every flower all over with an eagle eye. However, usually sap under the leaf means there is a pest somewhere nearby on that or a nearby leaf. If you use a systemic you are more likely to get them, since they can spread all over, even below the medium. Be sure to spray a lot of stuff in the leaf junction as they can get in there pretty far and you can't always bend the leaf far enough back to see them. Think of it as a safari. :)

Good call Carolb! Take a look at this link and see if you think these are the critters. bd74- yours are definitely one of the black thrip family. Here is a link that might be useful: Cuban Laurel Thrips