Yellowing around edge of leaf…

[lambo1972]

Hello all! 2 of the phals that have had for quite some time just recently in the last 6 months or so are showing some yellowing on the edges of their leaves. What are possible causes or most likely cause for this? Both of them are smaller with flowers maybe 1 1/2 to 2”. They are kept in different locations. I have always found my phals to be pretty hardy. The one shown in the pics was replanted back in October and then set 2 pretty flower spikes and is making new roots too. Some of the leaves are wrinkly too bit I’m working on that. I am trying to get better with orchids and learn as it is becoming a full on hobby. Thank you for the advice as always!