Brown sticky residue on phal

[Orchidrhia]

Hi everyone! I noticed this brown sticky residue or sap on the leaf of my phal yesterday. Cleaned it off and it’s there again today. I can’t see any visible pests or bugs and strangely, it’s only on one leaf. I thought it was happy sap at first but from what I found online, isn’t happy sap usually clear? And not brown? Hope someone can enlighten me on what this is. This orchid has been doing so well lately, so I hope it’s nothing serious. Thanks!