Looks like sunburn. Those portions of the leaves will turn brown and paper thin. While it looks unsightly the damage has already been done and it should not progress any further. Just keep an eye out for any secondary infections like bacterial infection and fungus.
Phals dont like direct sun, so in the future if you should put them outside, a shaded spot would be best.
New leaves will eventually grown to replace and cover these.
Good luck with their recovery!
Judi
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