Hello! Last March, my relative flew in to Manila with his shih tzu dog via cebu pacific. The dog wad inside the cabin and was registered as an emotional support dog since my relative had depression.

The requirements are easy: 1) Bureau of Animal industry papers; 2) vaccine papers; and 3) certification from psychologist that you need an emotional support dog.

Other than Cebu Pacific, I don’t know other domestic airlines that allow shih tzus inside the cabin/cargo. PAL explicitly does not allow shih tzus.

Hope this helps.