Froglights should follow this type of rotation https://wiki.bedrock.dev/blocks/rotatable-blocks#log-rotation
You can use minecraft:geometry.full_block rather than making your own model
I think that froglights also have the top texture applied to the bottom, so you should add that to your material instances:
"minecraft:material_instances": {
"down": "up",
"up": {
"texture": "blossom_froglight_top",
"render_method": "opaque",
"face_dimming": false,
"ambient_occlusion": false
},
"*": {
"texture": "blossom_froglight",
"render_method": "opaque",
"face_dimming": false,
"ambient_occlusion": false
}
}